How can I get more sleep?

I'm always feeling obligated to stay up "just a little longer," and when I do eventually get in bed, I'm ending up staring at the ceiling for hours. I'm very sensitive to noises that may go on in the night, and it can prevent me from sleeping. It's very hard for me to relax at night, and I'm always feeling that I need to get up and do something. Thanks to this, I've gotten dark circles under my eyes and I've gradually been doing worse in my studies, I always feel like I'm in a haze, and I'm dozing off when I should be wide awake. So, how can I get more sleep?