1. Have Masses offered for them.
2. Pray the Rosary and/or the Divine Mercy Chaplet.
3. Pray the Stations of the Cross.
4. Offer up little sacrifices.
5. Fast
6. Spread devotion to them.
7. Attend Eucharistic Adoration and pray for them.
8. Gain all the indulgences you can, and apply them to the Holy Souls.

Remember, anything you do to help the Holy Souls is an act of charity
and it is one done to those who are the most in need of your assist-
ance, since they can no longer help themselves, and are TOTALLY and
COMPLETELY dependent on us to help them. If we release a soul from
there, it will be eternally grateful, and will intercede with God for
us, while we yet live on earth and when, or if, we go there. 

Prayers for (and to) the Holy Souls in Purgatory:

 
***A Prayer for the Souls in Purgatory

 O most gentle Heart of Jesus, ever present in the Blessed Sacrament,
ever consumed with burning love for the poor captive souls in Purga-
tory, have mercy on the souls of Thy departed servants. Be not severe
in Thy judgments, but let some drops of Thy Precious Blood fall upon
the devouring flames. And do Thou, O Merciful Saviour, send Thy holy
angels to conduct them to a place of refreshment, light, and peace.
Amen. 

***A Prayer for the Dead

 O God, the Creator and Redeemer of all the faithful, grant unto the 
souls of Thy departed servants full remission of all their sins, that
through the help of our pious supplications they may obtain that par-
don they have always desired, Thou who livest and reignest world with-
out end. Amen.

V. Eternal rest grant unto them, O Lord.
R. And let perpetual light shine upon them.
V. May they rest in peace. Amen.
R. And may the souls of all the faithful departed, through the mercy
   og God, rest in peace. Amen.

***A Prayer for our Dear Departed

 O Good Jesus, Whose loving Heart was ever troubled by the sorrows of
others, look with pity on the souls of our dear ones in Purgatory. O
Thou who didst "love Thine own," hear our cry for mercy, and grant 
that those whom Thou hast called from our homes and hearts may soon
enjoy everlasting rest in the home of Thy love in Heaven. Amen.

V. Eternal Rest grant unto them, O Lord.
R. And let perpetual light shine upon them. Amen.

***A Prayer for Deceased Parents

 O God, who hast commanded us to honor our father and our mother, in
Thy mercy have pity on the souls of my father and mother, and forgive
them their trespasses, and make me to see them again in the joy of
everlasting brightness. Through Christ our Lord. Amen.
                                       - The Roman Missal

***A Prayer to Jesus and Mary

 O most loving Jesus, I humbly beseech Thee that Thou wouldst Thyself
offer to Thine eternal Father, on behalf of the Holy Souls in Purga-
tory, Thy Most Precious Blood, which poured forth from the Sacred 
Wounds of Thine adorable Body, together with Thine agony and death.
And do thou likewise, O sorrowful Virgin Mary, present unto the 
Heavenly Father, together with the dolorous passion of thy dear Son,
thine own sighs and tears, and all the sorrows thou didst suffer in
His suffering, in order that, through the merits of the same, refresh-
ment may be granted to the souls now suffering in the fiery torments
of Purgatory, so that, being delivered from that painful prison, they
may be clothed with glory in Heaven, there to sing the mercies of God
for ever and ever. Amen.
 Absolve, O Lord, the souls of all the faithful departed from every
bond of sin, that by Thy gracious assistance they may deserve to 
escape the judgment of vengeance and enjoy the blessedness of ever-
lasting light. Amen.

V. Eternal rest grant unto them, O Lord.
R. And let perpetual light shine upon them.
V. From the gates of Hell,
R. Deliver their souls, O Lord.
V. May they rest in peace.
R. Amen.
V. O Lord, hear my prayer.
R. And let my cry come to unto Thee.

                           Let us pray

 O God, the Creator and Redeemer of all the faithful, grant unto the 
souls of Thy servants and handmaids the remission of all their sins,
that through our devout supplications they may obtain the pardon they
have always desired, Thou Who livest and reignest world without end. 
Amen.
 Eternal rest, etc.

***A Prayer for the Poor Souls

 My Jesus, by the sorrows Thou didst suffer in Thine agony in the Gar-
gen, in Thy scourging and crowning with thorns, on the way to Calvary,
and in Thy crucifixion and death, have mercy on the souls in Purga-
tory, and especially those that are most forsaken; do Thou deliver 
them from the dire torments they endure; call them and admit them to
Thy most sweet embrace in Paradise. Amen.
 Our Father, Hail Mary, Glory Be.

V. Eternal Rest grant unto them, O Lord,
R. And let perpetual light shine upon them.
V. May the divine assistance remain always with us.
R. And may the souls of the faithful departed, through the mercy of 
   God, rest in peace. Amen.


***Prayer for the Poor Souls from the Canon of the Mass

 Remember, O Lord, Thy servants and handmaids, N. and N., who have 
gone before us marked with the sign of faith and rest in the sleep of
peace. To these, O Lord, and to all who rest in Christ, grant, we be-
seech Thee, a place of comfort, light, and peace. Through the same 
Christ our Lord. Amen.

***Prayer to God the Father

 Eternal Father, I offer Thee the Precious Blood of Jesus Christ in
satisfaction for my sins, in supplication for the Holy Souls in Purga-
tory and for the needs of the Holy Church. Amen.

***Prayer of St. Gertrude the Great

 O Eternal Father, I offer Thee the Most Precious Blood of Thy Divine
Son, Jesus, in union with the Mases said throughout the world today,
for all the Holy Souldin Purgatory and for sinners everywhere - for 
sinners in the Universal Church, for those in my own home and for
those within my family. Amen.

***A Novena for the Poor Souls (Prayers from the Raccolta, 594-595)

 Prayer to be said every day of the Novena

 V. O Lord, hear my prayer;
 R. And let my cry come unto Thee.

 O God, the Creator and Redeemer of all the faithful, grant unto the 
souls of Thy servants and handmaids the remission of all their sins,
that through our devout supplications they may obtain the pardon they
have always desired, Who livest and reignest, world without end. Amen.
 Eternal rest, etc.

 SUNDAY
 
 O Lord God Almighty, I beseech Thee by the Precious Blood which Thy
divine Son Jesus shed in the Garden, deliver the souls in Purgatory,
and especially that one which is the most forsaken of all, and bring 
it into Thy glory, where it may praise and bles Thee forever. Amen.
 Our Father, Hail Mary, Glory Be. Eternal rest, etc.

 MONDAY
 
 O Lord God Almighty, I beseech Thee by the Precious Blood which Thy
divine Son Jesus shed in His cruel scourging, deliver the souls in
Purgatory, and among them all, especially that soul which is nearest
to its entrance into Thy glory, that it may soon begin to praise Thee
and bless Thee forever. Amen.
 Our Father, Hail Mary, Glory Be. Eternal rest, etc.

 TUESDAY

 O Lord God Almighty, I beseech Thee by the Precious Blood of Thy
divine Son Jesus that was shed in His bitter crowning with thorns, 
deliver the souls in Purgatory, and among them all, particulary that
soul which is in the greatest need of our prayers, in order that it
may not long be delayed in praising Thee in Thy glory and blessing
Thee forever. Amen.
 Our Father, Hail Mary, Glory Be. Eternal rest, etc.

 WEDNESDAY

 O Lord God Almighty, I beseech Thee by the Precious Blood of Thy 
divine Son Jesus that was shed in the streets of Jerusalem, whilst He
carried on His sacred shoulders the heavy burden of the Cross, deliver
the souls in Purgatory, and especially that one which is richest in
merits in Thy sight, so that, having attained the high place in glory
to which it is destined, it may praise Thee triumphantly and bless
Thee forever. Amen.
 Our Father, Hail Mary, Glory Be. Eternal rest, etc.

 THURSDAY

 O Lord God Almighty, I beseech Thee by the Precious Body and Blood of
Thy divine Son Jesus, which He Himself, on the night before His Pass-
ion, gave as meat and drink to His beloved Apostles and bequeathed to
His holy Church to be the perpetual Sacrifice and life-giving nourish-
ment of His faithful people, deliver the souls in Purgatory, but most 
of all, that soul which was most devoted to this Mystery of infinite
love, in order that it may praise Thee therefore, together with Thy
divine Son and the Holy ghost in thy glory forever. Amen.
 Our Father, Hail Mary, Glory Be. Eternal rest, etc.

 FRIDAY

 O Lord God Almighty, I beseech Thee by the Precious Blood which Jesus
Thy divine Son did shed this day upon the tree of the Cross, especi-
ally from His sacred hands and feet, deliver the souls in Purgatory,
and particularly that soul for whom I am most bound to pray, in order
that I may not be the cause which hinders Thee from admitting it 
quickly to the possession of Thy glory, where it may praise Thee and
bless Thee forevermore. Amen.
 Our Father, Hail Mary, Glory Be. Eternal rest, etc.

 SATURDAY

 O Lord God Almighty, I beseech Thee by the Precious Blood which gush-
ed forth from the sacred side of Thy divine Son Jesus in the presence
of and to the great sorrow of His most holy Mother, deliver the souls
in Purgatory, and among them all, especially that soul which has been
most devout to this noble Lady, that it may come quickly into Thy
glory, there to praise Thee in her, and her in Thee, through all the 
ages. Amen.
 Our Father, Hail Mary, Glory Be. Eternal rest, etc.

***A Short and Efficacious Prayer for the Faithful Departed

 O Most compassionate Jesus, have mercy on the souls detained in Purg-
atory, for whose redemption Thou didst take upon Thyself our nature
and endure a bitter death. Mercifully hear their sighs, look with pity
upon the tears which they now shed before Thee, and by virtue of Thy
Passion, release them from the pains due to their sins. O most merci-
ful Jesus, let Thy Precious Blood reach down into Purgatory and re-
fresh and revive the captive souls who suffer there. Stretch out to
them Thy strong right hand, and bring them forth into the place of
refreshment, light and peace. Amen.
 
***A Prayer to the Poor Souls in Purgatory
 
 O holy souls in Purgatory, thou art the certain heirs of Heaven. 
Thou art most dear to Jesus, as the trophies of His Precious Blood,
and to Mary, Mother of Mercy. Obtain for me, through thine intercess-
ion, the grace to lead a holy life, to die a happy death, and to att-
ain to the blessedness of eternity in Heaven.
 Dear suffering souls, who long to be delivered in order to praise and
glorify God in Heaven, by thine unfailing pity, help me in the needs
which distress me at this time, particularly (here mention your
request), so that I may obtain relief and assistance from God.
 In gratitude for thine intercession, I offer to God on thy behalf the
satisfactory merits of my prayers, works, joys and sufferings of this
day (week, month, or whatever space of time you wish to designate.)
Amen.

Some Resources on Purgatory

The Way of the Cross for the Holy Souls in Purgatory 

"It is a holy and wholesome thought to pray for the dead, that they may be loosed from sins."  - 2 Mach. 12:46 

An Act of Contrition 

My Jesus! I love Thee above all things. I hate and detest all my sins, because by them I have offended Thee. The holy indulgences, the fruits and merits of this devotion I intend to gain for the souls in Purgatory, in particular for those who in life were near and dear to me, and also for those for whom I am, in a special way, obliged to pray. 

O Mary, my merciful Mother and the Mother of the poor souls in Purgatory accompany me, by your intercession, on this journey.   

[Station theme - I to XIV]

V. We adore Thee, O Christ, and we bless Thee. 
R. Because by Thy holy cross, Thou hast redeemed the world.   

[Prayers of Stations I to XIV]

My Jesus, mercy!
Our Father.
Hail Mary.
Eternal rest grant unto them, O Lord - and let perpetual light shine upon them. Merciful Jesus, grant them eternal rest

The First Station
Jesus is Condemned to Death 

O my innocent Jesus, to free me from eternal death, Thou allowed Thyself to be condemned by a pagan judge to the death of the cross. Give me a hatred for sin and the grace to live that I may one day obtain from Thee a merciful sentence.  The poor souls in Purgatory have already been judged. Through Thy mercy they have escaped hell, yet on account of their sins Thy justice has con­demned them to the fire of Purgatory. O most merciful Jesus, have pity on them. Revoke the sentence of their exile and open to them the gates of heaven. 

The Second Station 
Jesus is Made to Bear His Cross 

O holy cross, you are the tree of life, the gate of heaven, our salvation and our only hope. Be my salvation at the hour of death. O Jesus, be mindful of Thy servants who have departed this life with this sign of Faith. Free them by the victorious power of Thy cross, with which Thou hast conquered death. Lead them into eternal life and happiness. 

The Third Station 
Jesus Falls for the First Time Under His Cross 

Through Thy weakness under the cross and the merits of this first fall, grant me perseverance in my good resolutions that I may always walk faithfully in Thy holy ways. The souls in Purgatory now suffer because they neglected and abused Thy graces in this life. They now realize that no sin-stained soul can see God. Have mercy, therefore, on them and cleanse them from all sin.  Through the intercession of Thy sorrowful Mother, deliver them from Purgatory. 

The Forth Station
Jesus Meets His Afflicted Mother 

O Heart of Mary! O heart of Jesus! I offer my life for my sins. May the sweet names of Jesus and Mary be on my lips and in my heart at the hour of my death. "O sweetest heart of Jesus, we implore that we may love Thee more and more." Sweet Heart of Mary, be our salvation."  Mother most sorrowful, merciful queen of the Holy Souls, into your hands I place my few merits and implore you to unite them with the infinite merits of your Son. Offer them to the eternal Godhead for those souls who are bound to me by ties of relationship.

The Fifth Station 
The Cyrenian Helps Jesus to Carry His Cross 

O my Jesus, I accept the cross, I embrace it. Let me help you to carry Thy cross, by being patient in all trials that may assail me. How many souls in Purgatory now regret their past impatience! But Thou, O Lord, be generous with them and remit that which still remains to be expiated. 

The Sixth Station 
Veronica Wipes the Face of Jesus 
 
Lord, Jesus Christ, Thou who hast left on Veronica's veil the impress of Thy blood-stained countenance, grant that the memory of Thy bitter passion and death may ever remain impressed on my soul. Have pity on the poor souls, made to Thy image and likeness and redeemed by Thy Most Precious Blood. Free them from all sin that they may enter heaven, to see Thee face to face forever and ever. 

The Seventh Station 
Jesus Falls the Second Time 

My sins have made Thy cross heavy, O Jesus. I detest them and firmly resolve to amend my life. 

Never permit me to separate myself from Thee again.  Have mercy, O Jesus, on those souls who now suffer the pains of Purgatory for mortal sins com­mitted in this life.  O clement Heart of Jesus, have compassion on them. 

The Eighth Station 
Jesus Comforts the Women of Jerusalem

Most compassionate Heart of Jesus! My Jesus, who said to the holy women: "Weep not over me, but weep for yourselves and for your children," make me weep for the ingratitude, which I have returned for Thy love. I wish to make amends in this life for my sins, that I may obtain pardon of them in the next.  Grant me a tender love for the souls in Purga­tory, especially for the souls of my relatives. In the future I promise to do what I have neglected through my forgetfulness and hardness of heart.

The Ninth Station 
Jesus Falls the Third Time  

Through this most painful fall, O Jesus, I ask Thee to deliver me from an unhappy death, which would plunge me into hell. From the power of the enemy deliver my immortal soul, and make me live and die in Thy grace. Look with mercy upon the poor souls doing penance in Purgatory. With tears and prayers they seek Thy help and mercy. Hear their prayers and lead them out of that place of punishment into the blessed peace of heaven, there to enjoy forever the splendor of Thy glory.

The Tenth Station 
Jesus is Stripped of His Garments 
 
My most blessed Redeemer, stripped of Thy garments for love of me, grant me holy mod­esty and purity.  Deliver me from all dangerous inclinations to created things: make me die to everything of this world, that at death separation from all earthly things may be easy. Of what benefit now are wealth and the pleasures of this world to the souls in Purgatory? Their bodies they had to leave to worms, and their wealth to heirs; only their works have followed them, the good to be rewarded, the evil to be punished.  O Lord, put an end to their suffering, do nor keep them any longer from the heredity of the saints, but pardon them and admit them into the realm of eternal bliss and happiness.

The Eleventh Station 
Jesus is Nailed to the Cross 

My most innocent Jesus, nailed to the cross for my sins, I beseech Thee, through the mer­its of Thy horrible suffering, to come to my aid in my last sickness and agony. Grant me the grace to receive in time Thy most holy Sacraments. Come to me then, O most Holy Viaticum, and pour upon my soul the patience of Thy Most Sacred Heart! And you, O Mary my Mother, console me in that hour and make sweet my sufferings, through the sorrow that pierced your heart at the crucifix­ion. Lamb of God, have mercy on the souls in Pur­gatory, whose sufferings are greater than those of the sick and dying. Spare them this agony, and through the merits of Thy
passion admit them into eternal dwellings.

The Twelfth Station 
Jesus Dies On the Cross  

Through Thy three hours' agony on the cross, grant me, O Jesus, a happy death. Take me when I am best prepared. In that hour fill my soul with holy sentiments of faith, hope and charity. Grant me true and perfect contrition for my sins and the grace to accept with Christian resignation my death with all its pains and sufferings.   May I leave this world invoking Thy most Holy Name. Mary Mother of Sorrows, refuge of the dying, be near me in my last agony. Remember, O most loving Jesus, the poor souls with that love with which you did give comfort to the good thief: "This day you shall be with me in Paradise." Call these souls into the kingdom of Thy glory, that they may praise Thee together with all the angels and saints forever and ever. 

The Thirteenth Station 
Jesus is Taken Down from the Cross 

Jesus, Thou whose soul did descend to the dead to announce peace to the just of the Old Testament, descend now amongst the poor souls who yearn for Thee; free them from the chains of their slavery and grant them the liberty of true children of God! O Mary, my Mother, may I, like Jesus, be placed in your arms at my departure from this world. Be with me at the tribunal of the Divine Judge that through your intercession, I may obtain a favorable sentence. Sweet Heart of Mary be my salvation! 

The Fourteenth Station         
Jesus is Laid in the Tomb 

Jesus, through the merits of Thy bitter pas­sion and death and through Thy glorious Resurrection, I beseech Thee, have compassion on the poor souls and grant them a happy and glorious admission into heaven. Let them enter into that peace so long desired; let them contemplate the splendor of the Beatific Vision; let them bless eternally Thy mercy. 

"Sweet Heart of Mary, be my salvation," when I myself shall be condemned to that place of torture, when my body will be in the cold earth and my soul in the fire of Purgatory. Most loving Mother, on that day save your child. Bring me quick relief and through your merits deliver me from the flames, that I may thank you in heaven, and with you & all the saints, adore and love Jesus, your beloved Son, who with the Father and the Holy Ghost
lives and reigns, true God, forever and ever. Amen. 

Closing Prayer
My crucified Redeemer, I offer Thee this devout exercise, which by Thy grace, I have just finished. Grant that the precious fruits of Thy death on the cross be not lost either for me or for the souls in Purgatory. Mary, Mother of Sorrows, place my petitions in the Heart of your beloved Son, so that I may be admitted into the kingdom of grace, there together with my dear ones, both living and dead, to be blessed eternally. O Gentlest Heart of Jesus, ever present in the Blessed Sacrament, ever consumed with burning love for the poor captive souls in Purgatory, have mercy on them. Be not severe in Thy judgments, but let some drops of Thy Precious Blood fall upon the devouring flames, and do Thou, O merciful Savior, send Thy angels to conduct them to a place of refreshment, light and peace. Amen.

Eternal rest grant unto them, O Lord, and let perpetual light shine upon them. Sacred Heart of Jesus, have mercy on them. Merciful Jesus, grant them eternal rest.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

This prayer below is not part of the Stations, however it is a very 
useful prayer:

A Covenant with God

  O my God, all my desire is before Thee, but, inasmuch as the necessities of life prevent the constant
application of my mind to Thy praise, I make with Thee this covenant, desiring that it may remain in
force throughout my life.
  With every beating of my heart; at every temptation; every time that I shall pass before a Cross or a
church; whenever I meet anyone; every time I breathe, or move, or speak, or act, or work, or suffer,
or pray, or eat, or drink, or rest, or recreate, I desire and intend to offer Thee, as many times as there 
are seconds in the day, grains of sand on the earth, and particles in the air, all the merits of OUR LORD
JESUS CHRIST, His fasting and penances, His Sacred Passion and Most Precious Blood, His humiliations
and death; all the Masses that have been, are being, or ever will be celebrated; all the merits, sorrows and
joys of the BLESSED VIRGIN MARY, and those of St. Joseph, and those of all the Saints; the labors of
all Apostles, the blood of martyrs, the purity of Virgins, the austerities of Penitents, the prayers of our
Holy Mother the Church; in a word, all the meritorious works that have been, are being, or ever will be
performed until the end of time.
  This offering I make to Thee, O my God, in order to obtain the pardon of all my sins; those of my 
relatives, friends, and enemies; those of  all infidels, heretics, Jews, and all bad Christians; for the
triumph of Thy Holy Church; the accomplishment of Thy Holy Will upon earth as in Heaven; the
acquisition of all virtues, especially____; the grace of a happy death; and the deliverance of all souls in
Purgatory, for whom I desire to gain all possible indulgences.
  By this offering, I desire to thank Thee for all the natural and supernatural benefits, known and unknown graces that have been, are being, or that shall be granted to myself, to my relations and friends, and to all
mankind, even until the end of time. In a word, I desire to make of the remainder of my life one long act of 
love, hoping in this manner to offer some reparation for the time I have lost in Thy service, and to render to Thine Infinite Majesty all the glory of which Thou hast been despoiled. Amen.

From "Charity for the Suffering Souls: An Explanation of the Catholic
Doctrine of Purgatory"  by Rev. John A. Nageleisen,  Pgs. 223-225
Published by Tan Books

 St. Leonard of Port Maurice exhorts us most earnestly to have Masses
celebrated for ourselves during life time rather than after our 
death.