Well for starters, stop stressing about it, that's just going to make it worse.
Get a good serve of healthy carbs and magnesium (brown rice, veggies, or even in tablet form) like 60-90 minutes before bed. Glutamine (can be bought in powder) can also work wonders too.
But if it's more of a mental issue, some of these tips can help:
- Get off laptop, phones etc for 30 min before bed, it stimulates your brain way too much (plenty of research on this, google)
- Sit, lay or even meditate in a dark room for 10 minutes before trying to fall asleep
One thing that's especially helped me is to either write your thoughts on a piece of paper or write down the order of what I'm doing tomorrow down. Kind of like a brain clean out, you won't stress about forgetting anything or whatever because it's written down.
But seriously you'll probably have to distract your mind. What gets me knocked out 100% of the times is watching a movie at the end of the day on my laptop(lights off and adjusted brightness for night time) and 40 minutes in I'm knocked out(around midnight)
Although getting exposure to light before sleeping won't do any favors. Maybe you should check out some guided meditation on sleeping?