Make sure you stop drinking or eating anything with caffeine or excessive sugar after about noon. That means coffee, tea, soda, and even chocolate.
This won't necessarily 100% cure the problem, but it will eliminate one reason why you might be having trouble sleeping.
A few more suggestions: if you have a TV in your room, turn it off when you want to sleep. Stop checking your phone maybe 15 - 30 minutes before you want to go to sleep. And if you play video games, stop them then, too.
Why? Because all of these can be stimulants as well.