Meditate. Try learning how to meditate. Meditation teaches you how to ease the clutter from your mind. A good technique is to use a mantra (repeat a word or phrase) in your mind over and over again. This helps you to block out random thoughts and just focus on the one phrase, such as "i feel calm and relaxed." you can also focus on your breathing or relaxing your muscles.
Slow down earlier. Common answers have been; don't eat or exercise too late at night, turn off the tv and computer an hour prior to going to sleep (really hard to do), limit or stop caffeine, nicotine and alcohol especially toward evening (harder yet), don't nap during the day and do something to relax prior to bedtime (meditation?). Reality says you can't do them all. One or two of these may help. Sleepy yet?