Going to sleep can be tricky sometimes, especially if you have had too much caffeine too late in the day or your mind is too busy. I have a few tricks to help me get to sleep in a timely manner:

1. Melatonin supplement -- extremely cheap and safe; set a timer on your phone and take 1-2mg about 1/2hr before you want to sleep.
2. Close one eye and keep the other open for about 15 seconds. It should naturally close itself, at which point both eyes will typically be in a state where they want to be closed. Repeat with the other eye if need be.
3. Imagine doing a backflip. Whatever mental scenery you could see before will be replaced with a new scene, typically a bit more vivid and immersive/dream like.
4. Do some math. Work your way through the multiplication tables, imagine different angles around the unit circle, etc. This will use up mental energy and make you "bored" in the way that often makes people fall asleep in math class. You can also simply count -- imagining the number symbols as you go.
5. If something is bugging you, get up and grab a pen. Write it down. Later you can shred it if it isn't important to your awake mind, or act on it if appropriate.
6. Think about something you learned recently. Try to think of any new implications that you didn't already think of. Your mind will be solving problems and creating new memories, so now is a good time to feed it something you would like to learn.