Whether we engage in prayer through memorized prayers, or through official liturgical prayer, the quality of our prayer life depends on the spiritual state of our heart.
The Catechism of the Catholic Church makes this clear in its section on prayer:
The Lord leads all persons by paths and in ways pleasing to him, and each believer responds according to his heart's resolve and the personal expressions of his prayer. However, Christian Tradition has retained three major expressions of prayer: vocal meditative, and contemplative. They have one basic trait in common: composure of heart.
The Catechism further explains that two central keys for "composure of heart" are, "This vigilance in keeping the Word and dwelling in the presence of God makes these three expressions intense times in the life of prayer."
If we want to prepare our hearts for our life of prayer, we need to frequently turn to the Word of God and frequently practice the presence of God.
In general, prayer doesn't simply "happen" to most of us and we need to train our heart to listen to God's voice.
When we successfully prepare our heart for moments of prayer, we will experience a profound union with God that is a foreshadowing of the ultimate union with God in Heaven.