First thing to figure out is, what's keeping you awake. I usually find that either my body is awake, so I can't sleep, or my mind is going 100 miles an hour (maybe round in circles) and won't let me sleep.
Something that has sometimes worked for me is to get up and have a mini-"day". Eat something meal-like (peanut butter toast is good -- peanut butter has trytophan), somewhere with the light on, while sitting up, maybe even do some exercise, anything that will make your body tired. Then try all the traditional sleep things (ie. glass of milk), then go to bed again. Doesn't always work, but if you think you're going to be awake for two hours, sometimes you can put yourself to sleep in 45 minutes this way (ie. half hour up, maybe 15-30 minutes in bed going to sleep).
If you have the flexibility, and just want to be less tired, you could also try polyphasic sleep:
http://www.sleepingschedules.com/