How can I get a better nights sleep?

I need the have a lot of sleep because im a very active person but lately i haven't been able to get a good nights sleep (nightmares, waking up at 2 am, not being able to fall asleep etc.) I dont know what is causing this but i really need help because so far none of my ideas have worked (warm milk before bed, heat pad to warm up the bed, relaxing before trying to fall asleep etc.)