studies say you should put away the computer/phone at least an hour before heading to bed (but 30 minutes is better than nothing)
no exercise in the evening
no food a few hours before going to bed
bedroom should be as dark as possible

when I can't sleep (either fall asleep to begin with or waking up in the night and not immediately falling back asleep), I try to tell myself, "hey, at least you're in bed, doing nothing - you'd be happy about that in XX when you have to get up" to calm myself down and get my brain to stop fretting about not sleeping