Some good advice here( although, I would avoid drug-based solutions as much as possible). One thing I would add that doesn't get mentioned around this problem is to stop trying to sleep. It sounds backwards but, what happens if I ask you to close your eyes right now, and absolutely, under no circumstance must you think of pizza. Just for 10 seconds, whatever you do, you can do anything else you want but you must not visualize or think even the faintest thought or words or pictures in the mind, regarding pizza. Ready? Go.
What happens?
So if you do this experiment, you'll find that doing things by force often has a tendency to cause them to fail somehow. A lot of things in life are like this. Sleep is like this, where the more you "try" to sleep, you more restless you become. So just give up your struggle to sleep completely once you see it present. The moment you notice that you're actively trying to fall asleep, just stop. Give up. We're just going to lay here, there's absolutely no need or no desire to fall asleep, if we don't fall asleep that's perfectly fine. Make a resolution to fully accept that. It can often be enough that once you stop fighting with sleep, that is when you fall asleep.