I don't have any advice on stopping you from waking up, but my favourite way to get back to sleep quickly is to lie on your back and concentrate on your breathing. You then think really hard about the little toes on each of your feet - tense them up then relax them in time with your breathing- then let them relax as though they are dropping into the mattress. Then do the same with your second smallest toes, third, fourth, then big toes, then feet, then ankles, etc, etc all the way up your body - this way you are keeping your mind busy but with such mundane things that it's not really overactive, and you are relaxing your body at the same time.

Sorry for the long winded description, but you get the idea!