Day one - pray for all mankind, especially sinners:
"Today bring to Me all mankind, especially all sinners, and immerse them in the ocean of My mercy. In this way you will console Me in the bitter grief into which the loss of souls plunges Me." - from the diary of St. Faustina
Most Merciful Jesus, whose very nature it is to have compassion on us and to forgive us, do not look upon our sins but upon our trust which we place in Your infinite goodness. Receive us all into the abode of Your Most Compassionate Heart, and never let us escape from It. We beg this of You by Your love which unites You to the Father and the Holy Spirit.
Eternal Father, turn Your merciful gaze upon all mankind and especially upon poor sinners, all enfolded in the Most Compassionate Heart of Jesus. For the sake of His sorrowful Passion show us Your mercy, that we may praise the omnipotence of Your mercy for ever and ever. Amen.
Read HERE about the Divine Mercy Sunday Indulgence.