For those who already pray the Rosary, a simple way to add a prayer for priests is to add this prayer after each decade (following the Fatima decade prayer). It could also be prayed whenever inspired by the Holy Spirit, apart from the Rosary.
DECADE PRAYER FOR PRIESTS
God, our Father,
please send us holy priests,
all for the Sacred and Eucharistic Heart of Jesus,
all for the Sorrowful and Immaculate Heart of Mary,
in union with Saint Joseph.
Mary, Mother of Jesus Christ, Eternal High Priest, Mother of all priests, and our Mother, please help us to respond generously to the Holy Spirit's request, through the voice of His Church, to offer up to God Eucharistic adoration for priests. Amen.