One: Learn how to turn your brain off.
Chances are when you cant fall asleep it is because your brain is constantly going.
The trick here is to turn your mind off to the point where you can sleep.
This is hard for a lot of people especially if there is something big going on the next day or if you had a busy day before.
Do this by taking deep breathes and concentrate on something repetitive, such as running across a field or thinking of one act such as walking, or breathing, or swimming.
Two: Once you have tried to shut off your mind and that doesn't work, it is important to relax your body as well.
You can do this by trying to relax your body and put it in a somewhat of a meditation state.
This can be reaches by taking deep breathes in a rhythmic fashion.
Either by feeling yourself relax and soften deep into the bed, this will allow your muscles to relax and your body to feel tired as well.
Three: If these two steps above don't work for you.
You should try this technique.
Start at your toes and flex them, hold that flex for 5 seconds, than soften and relax.
After that you want to slowly move up, start with your pinky toe, and continue on up your body.
Take your time and stay on track.
Your mind will soon get tired of relaxing every muscle, and if you do it slow enough you will fall asleep before you get to your neck.