Prayer is the cornerstone for living a Christian life. There are almost as many ways to pray as there are Christians, but all Christians have prayer as a constant in their life in some way. If prayer is no longer a part of your life, you likely need to take a close look at your faith. A lack of prayer in your life is generally indicative as a lack of interest in having a real relationship with God. This, in turn, is the death knell for belief.
You are never too busy to pray. If you feel that you are too busy to pray but sincerely want to, reevaluate how you pray. Instead of making a big production of it or setting aside large chucks of time to devote exclusively to prayer, sneak prayer in to the parts of your day that you spend simply sitting around, such as when water is boiling or you are waiting for the train. It is far better to pray a little bit here and there than to never pray at all.