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There are herbal "relaxants", if you have any interest in going that direction. Chamomile teas, and "sleepy" teas, as they are often called.
If that's not of interest to you, the best help I've found, non drug related, is as follows:
1) do not nap during the day, no matter how tired you are. If you absolutely must: restrict it to 1 hour, and keep the wakeup time before 3pm.
2) fresh air and exercise. Go for a long walk, or even just sit outside for an hour or two...but make sure this is several hours before you want to go to sleep, also, as exercise invigorates before it tires us out.
3) try to write out every single thought in your head, in as much details as possible. It can often help us relax if we feel we've gotten our thoughts out of our own head
4) make sure you have a sleep routine. Go to bed at the same time every night, wake up at or around the same time every day. At a certain time, prior to going to bed: start dimming lights, and even computer/tv screens, if you can (about an hour before bedtime is usually good, but if you want to start dimming things earlier than that, feel free!). Darkness signals to your brain that it's time to sleep, so it starts shutting down, and releasing the appropriate chemicals/hormones for sleep.
5) take vitamin D supplements, when you wake up (with your first meal). It will give you a ton more energy (and level your moods, help prevent cancer, boost your immune system, increase your intestinal health, increase (ladies) vaginal health, make your skin/complexion healthier...I could go on lol), and it will help you to have the energy when you are supposed to (during the day), so you burn energy, and are actually tired enough to sleep when you're supposed to (night, obviously).
6) If you can't sleep - get out of bed. Go sit in the living room, go get a drink (milk is good...calcium helps you sleep...it doesn't have to be warm, though lol), go to the bathroom, whatever. The longer you are in your bed, unable to sleep, the more you associate bed with not sleeping, and not being able to sleep. Also, try to use your bed for sleep only (well, not ONLY ;) haha)...avoid doing anything stressful in or on your bed, ever (ie schoolwork, work-work). Your brain will make the association, when you're in bed, and it will head to the work-headspace.
Oh, and try not to eat within an hour of going to bed. Food gives us energy, and kickstarts our digestive system, which makes it more difficult to sleep. There is also the thought that certain foods can cause vivid dreams which leave you feeling unrested when you wake up...I don't know if that's true or not, but, you never know!