Drink a glass of milk to warm you and will also help you fall asleep. Try also to calm down and prepare your mind to sleep by adjusting the lighting and preparing the bed. Get more tips on how to fall asleep on http://www.wikihow.com/Fall-Asleep-Easier-As-a-Teen.
Get room as dark as you can and lay down on your side taking deep breaths in thru your nose out the mouth, do it 16 times then flip to the other side and repeat. If that doesn't work try laying down relaxing each part of your body from head to toes like start with the head, then face and jaw, then shoulders and arms.... Keep going till you get to the toes... I usually fall asleep before I can even get to toes!