Things that will keep you awake: orange juice (potassium, so bananas count too), caffeine, exercise, naps, irregular sleep schedules, stress, I'm sure lots else.
Don't exercise within a few hours of your planned bed time otherwise it will help keep you awake. That's the normal recommendation at least, but I do know people who like to nap after a workout.....whatever works for you.
If I nap in the day, I can't sleep at night.
If I sleep in that morning, I can't go to sleep as early at night. The earlier I wake up the earlier I can go to bed.
I can never sleep before anything that stresses me much, such as a test when I was in school, my first day of work, things such as that. Also when I'm excited about something I can't sleep as well, such as dreaming of doing things to my car when I get money....
If you can't get to sleep, get up and do something for a little while. Make the time productive if you can. Usually for insomnia they recommend that you go ahead and get up and do something if you can't sleep, maybe do it for 30 minutes or so, then try sleeping again.
The more I want/need to sleep, the less I can. The less I need to sleep, the more I can. I can sleep through class or work all day long....
b