These are ideas I passed on to aircrew when I worked at CFSSAT and taught about sleep physiology. You might want to try:
a) Writing down a list of things you "need" to do for the next day. That way, you're not worrying about forgetting to do them while trying to fall asleep.
b) Have a look at the bed and pillow you sleep with. You spend about a third of your life sleeping, so throw a little more money in your sleeping surface than you throw into a pair of running shoes.
c) Get into a steady routine that you follow before going to bed...whatever works for you. For example, brush your teeth, read a book for fifteen minutes in an easy chair, drink a glass of water and get into bed.
d) If you have a TV in your bedroom, get it out of there. The bed should only be used for sleeping, and that other thing, and I don't mean making small forts. (Body associates the prone position with sleeping, which is why people get tired watching a TV from the bed.)
e) When you go to sleep, relax the body and clear your head of any thoughts. If you find that you can't clear your head, concentrate on saying a single word repetitively when you exhale...I use "sleep". You can also try concentrating/relaxing...make your body numb from the toes and then gradually move up your legs, truck, etc.
f) If you don't fall asleep within about 20 or 30 minutes, get up and do something else. Lying in bed, thinking about how you can't sleep isn't going to help matters.
g) Avoid taking any caffeine drinks within four to six hours of the time you want to go to sleep.
h) Stick to a regular sleep schedule. That means *not* sleeping in on the weekends. What a lot people end up doing is taking an hour+ long nap when they get home from work/school, which keeps them from getting sleepy at around 2300 hrs.
Hopefully something in that list can help you out.