I'm just a third year psychology student so don't take me as an expert, but there are a number of things that are thought to help mild insomniacs like me (though they aren't always terribly easy to do - and can be impossible in certain cases). As nothing I mention involves drugs or potentially hazardous activities, I think I'm safe in mentioning:
The no. 1 suggestion is to follow a stricter sleeping schedule. Rise and fall with the sun is preferably, but even just getting up at 7am to 8am every day and sleeping from 10pm to 11pm every night (including weekends). Followed by that is leaving caffeine, nicotine and other stimulants alone - cutting back somewhat if you don't want to quit. I've also heard that exercising within hours of bed can be a problem.
On a personal note, I've found it best to get up if I can't get to sleep in a half hour. Be up for about a half hour to forty five minutes doing something mind-numbing and then attempting to sleep again. Personally, the pressure of getting to sleep can be what keeps me awake sometimes - my friend's four-room flat is a nightmare (tiny bathroom ensuite attached to his bedroom and a tiny kitchen attached to the lounge room) because it means that I can't even get up and read without disturbing somebody.