A busy brain will keep you awake. Whether you are worrying or excited about something, trying to still your mind is rather like trying not to think of a pink elephant; you can't. Instead, fill your head with one of the following alternatives. Pick whichever you prefer...
Consciously choose to set aside whatever you are thinking about to make way for trying to think of an animal beginning with each letter of the alphabet. If you manage to get all the way to a zebra, begin again with different animals. When you get bored with animals, substitute boys' names, girls' names, trees, plants, music... Don't worry that this will keep you awake; the chances are you'll not get much beyond kangaroos, Kyle, Kylie, Kapok, Kale or Kaleidoscope!
2. PROGRESSIVE RELAXATION
Get as comfortable as you can. Breathe in slowly and deeply. Focus on your feet. Tense up your toes, then as you slowly breathe out, let them relax. Now repeat, focusing in turn on your ankles, calves, knees and so on, all the way up to your head. Keep your breathing slow and deep. Feel yourself relaxing as you work your way up your body. Repeat until you fall asleep.
3. SLEEP INDUCTION
Here's a link to an audio recording that will send you to sleep.
Sometimes all we need to get over is the peace of mind that comes from appreciating just how fortunate and safe we are. One by one, spend a moment considering all the things for which you can feel grateful: the security of your home, the food you have consumed, your friends, your health, your creativity...
5. RECORD YOUR IDEAS
If great ideas keep popping into your head to keep you awake, instead of considering them there and then, write them down. Keep a notebook and pencil beside your bed. Writing them down means you won't forget them, and you'll be able to devote better attention to them tomorrow when you're wide awake.