When that happens to me it's often because I'm ruminating about something, can't get it out of my mind and relax. If that's what's keeping you up, CBT (cognitive behavorial therapy) techniques can help to stop that thought pattern, or just taking some daily action (any concrete action besides just turning it over in your mind) towards resolving the thing you're thinking about can help.

White noise sometimes helps me sleep too, especially after waking up in the middle of the night.