Whenever I have problems with sleep I know something is going on inside me that needs to be resolved.
Do you feel calm or anxious? Do you have thoughts whirling about in your head or just feel sleepless? TSUKIKO had good advice. Eat healthy, don't eat anything several hours before you go to bed, get plenty of exercise. I'd add "Meditate". Don't read or watch tv/movies, read forums, play games at least 30-60 minutes before you go to bed. Try to just sit and "not think". Listen to quiet music, watch a candle...this time of the year, if you have a Christmas tree...watch the lights!
Quieting the mind can help depending on what is going on inside you.