When you're facing this trouble, a lot of it is lifestyle change.
Try and make a point to exercise regularly so you will be physically tired at night.
Leave your self an hour or two before you go to sleep at night to relax and read or do other activities you find soothing. Turn off the tv, the computer, and just let your body tune down.
When you're still having a lot of trouble, I find a warm bath as a great way to help me calm down and get my body to sleep.
Also, get yourself on a schedule. You might be tired the first few days after not sleeping well, but avoid naps and make it to the night.
Finally, don't stress it. The more worried you get about sleeping, the harder it will be.