The devotion of the three Hail Mary's – said morning and evening to honour the Immaculata, for the grace to avoid mortal sin – is an excellent and Catholic custom, especially propagated by St Leonard of Port Maurice.
According to the wise counsel of St Alphonso, after each Ave, say, "By thy pure and immaculate conception, O Mary, make my body pure and my soul holy." (Per tuam puram et immaculatam conceptionem, O Maria, redde purum corpus meum et sanctam animal meam.)
I like to also add, in honour of Mary Immaculate, the prayer of the Miraculous Medal: "O Mary conceived without sin, pray for us who have recourse to thee."
Ave Maria purissima!