It sounds as if humility is a prerequisite for prayer. Are there other virtues that prepare the way for effective prayer?
Faith, hope, and love, therefore, lead the man of prayer to God. That is the man who believes, hopes, and desires is guided with regard to what he should ask the Lord by study of the Lord’s Prayer.
from St. Augustine Answers 101 Questions on Prayer by Fr. Ermatinger.
The virtues are those habits that dispose one to act in such a way that the action achieves its proper end. Prayer is the action, the end of which is the receiving of the good things of God that He wishes to give. If the action of prayer is approached without virtue, one will be less capable of receiving the good things of God. How is this so? If one approaches prayer with a spirit of pride, one will pray for the things that one desires, rather than what God desires to give. Further, if one prays pridefully, there will exist an inclination of some degree to reject the good things that God might answer the misguided prayer with.
Beyond humility, there is the virtue of obedience, which is the habit that encourages one to pray as God has commanded for what God has commanded. Obedience isn’t blind obedience, but it is derived from the virtues of faith, hope, and charity.
The Patre Nostre is one of the good things given by God to those who pray. The answered prayer was Teach us to pray.” It comes from Jesus’ own very lips and those who have the virtue of faith and know Jesus to be the incarnate Second Person of the Trinity, cling to it knowing by faith that the Patre Nostre is God’s answer to both how to pray and what to pray for. Hope then springs forth, for if God has Himself declared the how and what, then one hopes then to receive those good things promised by God. Is not God good? Has He not promised? Will one then not receive? From here, comes the virtue of charity even though it has already been present. What is charity? Charity is a form of friendship that exists by sharing in God’s eternal goodness. It is the receiving of and participating in God’s good things, ultimately His own life. Charity is present because, by grace through faith, one already has received the Patre Nostre as prayer given by God containing the how-tos and what-fors of prayer, and because, by grace through hope, one looks forward to receiving that which God is promising to give to those that pray. Charity is being present and shall be present because, again by God’s own free gift, one is receiving and shall receive by the working out of the life of friendship with God, His very life, which is charity itself. All this by prayer for those so prepared by the virtues bestowed by God.