This form of prayer consists in saying a short phrase -- perhaps even one word -- over and over. Through repetition, the content of the phrase should pass from the lips to the head to the heart, and thus become an abiding attitude in one's stance toward life and God. There are three ways this can be practiced:
The phrase can be repeated over and over in one session of prayer. When this is done, the words are coordinated with breathing in order to establish a rhythm. For example, half the phrase can be recited (mentally) while breathing in, the other half while breathing out. Or one word (or unit that goes together: e.g. "the grace... of Our Lord... Jesus Christ") can be said with each breath. As the words are recited, the mind dwells on their meaning and the heart savors them appreciatively.
The phrase can be recited frequently throughout the day, in order to remain conscious of the theme of the day. This form of prayer, called in Christian tradition "the Jesus prayer" or sometimes "ejaculatory prayer," is useful for countering temptation or acquiring some habitual attitude of heart. For example, to say frequently throughout the day, "Sacred Heart of Jesus, I place my trust in you" is a way to fight off anxiety and grow in trust in God. Said frequently enough, the phrase can become a refrain in one's head and an abiding orientation of one's heart.
The two ways can be combined: one can recite the phrase prayerfully over and over during a period of prayer, then try to keep reciting it prayerfully throughout the day.