The Responsorial Psalm for the Mass for the Friday after Ash Wednesday is Psalm 51. Rather that revisit it I shall just mention that it is pretty much the perfect prayer (after the Lord’s Prayer) for penance and conversion.
I had earlier written a series of meditations on Psalm 51, they can be found here (they appear in reverse order, so you will have to scroll way down to get to the beginning, then scroll up. Perhaps they can form a Lenten Friday meditation?"The Stations of the Cross for Alcoholics"