Jesus gave to Saint Faustina for her own personal use the Novena to The Divine Mercy. He asked that the Feast of The Divine Mercy be preceded by this Novena, which would begin on Good Friday.

Conditions for obtaining the extraordinary graces from praying The Novena. (complete cleansing of all sins and punishment due to sin) starting on Good Friday:

Attend Mass on Divine Mercy Sunday and receive communion.
Contemplate the Redemption as the greatest Revelation of Divine Mercy.
Go to confession on Divine Mercy Sunday, or within 8 days before or after Divine Mercy Sunday.
Perform an Act of Mercy (deed, word, prayer, forgiving, comforting; corporal works of mercy; prayers for mercy for the world)

Jesus I Trust In You