3. If you really can't get to sleep
There are a couple of options here. One is to use the time to relax. In other words, abandon all attempts to sleep and allow yourself to just rest. In fact, don't even use the word 'sleep'. Tell yourself 'it doesn't matter if I don't sleep tonight; I'm just going to use the time to REST. It's a bit of trickery but you might be surprised how quickly you then get to sleep – particularly if you use the technique regularly.
If you really can't get to sleep, then get up and do something relaxing. Read a book, have a cup of camomile tea or warm milk, or even do some ironing as this can tire you. Don't lie in bed tossing and turning and making yourself frustrated and tired.