I am the queen of bad sleep, so here goes:

No more coke or any caffeine after midday! Even one can of coke can keep you buzzing past your bedtime so try to give all caffeine a rest in the afternoons.

Don't exercise too late. A lot of people who play sport or have training at night are too hyper to sleep and take time to wind down.

Have a light evening meal so your body isn't still digesting food and working while you want to be sleeping.

Clear your mind before you go to bed. If you have any issues or problems, try to deal with them before you go bye byes.

If it's your bedtime and you don't feel like you'll get to sleep quickly, stay up and read (not a page-turning blockbuster, but something more relaxing!) and try going to bed a bit later. It's better than tossing and turning in bed and stressing out that you can't sleep.

Try to differentiate between mental and physical tiredness. You know that tiredness you get if you've been studying or concentrating all day - that's mental tiredness and doesn't help you get to sleep. But physical tiredness from exercise or outdoor work or running around between classes will help you sleep. Keeping active during the day is a great thing.

Good luck