I used to have a lot of trouble falling asleep, but this is what helps me.

If you've been lying in bed for a half hour or more, get out of bed. Get up and do something, as long as you're not watching TV or Redditting or playing a video game or otherwise staring at a glowing rectangle. Read a book or listen to music. After about 15 minutes, go back to bed. If you're still not asleep in half an hour, repeat until you do fall asleep. This will train you to get sleepy the moment your head hits the pillow and you will never have trouble sleeping again.