Our Lord made a number of promises to Saint Faustina when he gave her the Chaplet of Divine Mercy, and they are recorded in her diary.

"Say unceasingly the Chaplet that I have taught you. Whoever will recite it, they will receive great mercy at the hour of death. Priests will recommend it to sinners as their last hope of salvation. Even if there were a sinner most hardened, if he were to recite this chaplet only once, he would receive grace from My infinite mercy." (Diary, 687)

"It pleases me to grant everything souls ask of me by saying the chaplet. When hardened sinners say it, I will fill their souls with peace, and the hour of their death will be a happy one. Write this for the benefit of distressed souls; when a soul sees and realizes the gravity of its sins, when the whole abyss of the misery into which it immersed itself is displayed before its eyes, let it not despair, but with trust, let it throw itself into the arms of My mercy, as a child into the arms of its beloved mother. Tell them no soul that has called upon My mercy has been disappointed or brought to shame. I delight particularly in a soul that has placed its trust in My goodness. Write that when they say this Chaplet in the presence of the dying, I will stand between My father and the dying person, not as the Just Judge but as the Merciful Saviour." (Diary, 1541)

See http://www.ncregister.com/blog/mfenelon/why-should-you-pray-the-divine-mercy-chaplet for more.

Another list is found on fathersofmercy.com:

1. “The souls that say this chaplet will be embraced by My mercy during their lifetime and especially at the hour of their death.” (Diary, 754)

2. “When hardened sinners say it, I will fill their souls with peace, and the hour of their death will be a happy one.” (Diary, 1541)

3. “When they say this chaplet in the presence of the dying, I will stand between My Father and the dying person, not as a just Judge but as a merciful Savior.” (Diary, 1541)

4. “Whoever will recite it will receive great mercy at the hour of death.” (Diary, 687)

5. “Priests will recommend it to sinners as their last hope of salvation. Even if there were a sinner most hardened, if he were to recite this chaplet only once, he would receive grace from My infinite mercy....I desire to grant unimaginable graces to those souls who trust in My mercy.” (Diary, 687)

6. “To priests who proclaim and extol My mercy, I will give wondrous power; I will anoint their words and touch the hearts of those to whom they will speak.” (Diary, 1521)

7. “The prayer most pleasing to Me is prayer for the conversion for sinners. Know, my
daughter, that this prayer is always heard and answered.” (Diary, 1397)

8. “At three o’clock, implore My mercy, especially for sinners; and, if only for a brief moment, immerse yourself in My Passion, particularly in My abandonment at the moment of agony....I will refuse nothing to the soul that makes a request of Me
in virtue of My Passion.” (Diary, 1320; also, cf. Diary, 1572)

9. “Souls who spread the honor of My mercy...at the hour of death I will not be a Judge for them, but the Merciful Savior.” (Diary, 1075)

10. “I promise that the soul that will venerate this image (of the Divine Mercy) will not perish.” (Diary, 48).... “The two rays denote Blood and Water....These two rays issued from the very depths of My tender mercy when My agonized Heart was opened by a lance on the Cross. These rays shield souls from the wrath of My Father.” (Diary, 299)

11. “I desire that the Feast of Mercy...be solemnly celebrated on the first Sunday after
Easter.... The soul that will go to Confession and receive Holy Communion (in a state of grace on this day) shall obtain complete forgiveness of sins and punishment.” (Diary, 699)

12. “Through this chaplet you will obtain everything, if what you ask for is compatible with My will.” (Diary, 1731)

1. Make the Sign of the Cross

In the name of the Father, and of the Son, and of the Holy Spirit. Amen.

2. Optional Opening Prayers

You expired, Jesus, but the source of life gushed forth for souls, and the ocean of mercy opened up for the whole world. O Fount of Life, unfathomable Divine Mercy, envelop the whole world and empty Yourself out upon us.

(Repeat three times) 
O Blood and Water, which gushed forth from the Heart of Jesus as a fount of mercy for us, I trust in You!

3. Our Father

Our Father, Who art in heaven, hallowed be Thy name; Thy kingdom come; Thy will be done on earth as it is in heaven. Give us this day our daily bread; and forgive us our trespasses as we forgive those who trespass against us; and lead us not into temptation, but deliver us from evil, Amen.

4. Hail Mary

Hail Mary, full of grace. The Lord is with thee. Blessed art thou amongst women, and blessed is the fruit of thy womb, Jesus. Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death, Amen.

5. The Apostles’ Creed

I believe in God, the Father almighty, Creator of heaven and earth, and in Jesus Christ, His only Son, our Lord, who was conceived by the Holy Spirit, born of the Virgin Mary, suffered under Pontius Pilate, was crucified, died and was buried; He descended into hell; on the third day He rose again from the dead; He ascended into heaven, and is seated at the right hand of God the Father almighty; from there He will come to judge the living and the dead. I believe in the Holy Spirit, the holy catholic Church, the communion of saints, the forgiveness of sins, the resurrection of the body, and life everlasting. Amen.

6. The Eternal Father

Eternal Father, I offer you the Body and Blood, Soul and Divinity of Your Dearly Beloved Son, Our Lord, Jesus Christ, in atonement for our sins and those of the whole world.

7. On the 10 Small Beads of Each Decade

For the sake of His sorrowful Passion, have mercy on us and on the whole world.

8. Repeat for the remaining decades

Saying the "Eternal Father" (6) on the "Our Father" bead and then 10 "For the sake of His sorrowful Passion" (7) on the following "Hail Mary" beads.

9. Conclude with Holy God (Repeat three times)

Holy God, Holy Mighty One, Holy Immortal One, have mercy on us and on the whole world.

10. Optional Closing Prayer

Eternal God, in whom mercy is endless and the treasury of compassion — inexhaustible, look kindly upon us and increase Your mercy in us, that in difficult moments we might not despair nor become despondent, but with great confidence submit ourselves to Your holy will, which is Love and Mercy itself.