If I'm having trouble with a busy mind then a relaxation technique I find quite helpful is the following:
Get comfortable in bed, in whatever position you find most relaxing.
Focus in on the rhythm of your breathing - actively monitor your breath in, then out. As you breathe in, recite it in your mind, ditto as you breathe out.
Continue, just focussing on the breathing pattern - and don't let yourself get sidetracked by other thoughts that pop into your mind - push them to one side and re-focus on the breathing and reciting.
That's it!
This does take practice - and perserverence. It works on the basis that its always alot easier to do something than not do something - therefore you give your mind something active to do - but the rhythm is monotonous and therefore should be soporific, after a time. Because you are occupying your mind with something (reciting the breathing pattern) you can banish other distractions more easily and therefore let your brain eventually switch off.
Good luck
