Many people today do not see the need for regular, formal prayer. "I pray when I feel inspired to, when it is meaningful to me," they say. This attitude overlooks two important things: the purpose of prayer, and the need for practice.
One purpose of prayer is to increase your awareness of G-d in your life and the role that G-d plays in your life. If you only pray when you feel inspired (that is, when you are already aware of G-d), then you will not increase your awareness of G-d.
In addition, if you want to do something well, you have to practice it continually, even when you don't feel like doing it. This is as true of prayer as it is of playing a sport, playing a musical instrument, or writing. The sense of humility and awe of G-d that is essential to proper prayer does not come easily to modern man, and will not simply come to you when you feel the need to pray. If you wait until inspiration strikes, you will not have the skills you need to pray effectively. Before I started praying regularly, I found that when I wanted to pray, I didn't know how. I didn't know what to say, or how to say it, or how to establish the proper frame of mind. If you pray regularly, you will learn how to express yourself in prayer.