If you have a really hard time falling asleep you should check if you have any problems with your hormone balance.
I take melatonin tablets when I have to wake up early since my issues with falling asleep are because my body doesn't produce it when it should.
Otherwise, don't sit in front of the computer right before going to bed. (I fail this all the time).
Take a (warm) shower.
Make sure that your room isn't too hot.
If you can't sleep don't stare at your alarm clock or check the time (You'll just get even more stressed).