If you wake up during the night, try to avoid looking at your clock and registering the time. If you do this, you are more likely to start worrying about how little sleep you will get if you don't fall asleep again. This then reduces your chances of getting back to sleep even further!
Instead, lie on your back and try to consciously relax each part of your body starting from your toes and working up to your head and face. Breathe deeply from your diaphragm and tell yourself that it doesn't matter if you don't fall asleep and that you will just use the time to rest and relax.