I experimented with polyphasic sleep a few years ago and from that I have retained the ability to fall asleep quickly pretty much anywhere. My best trick is to pretend to be in REM sleep:P Find a comfortable position to sleep in, close your eyes and squint slightly while looking upwards, basically trying to look at the bridge of your nose. This should not hurt at all.
Forbid all thoughts of words and music.
Look for patterns in the random noise of your eyelids and try to “follow” it. Once you start seeing complete images you’re under way to dreamland. It’s ok to suddenly realize that you’re doing it and thus waking yourself up a little. Try again. Just relax, think about nothing and watch the pretty pictures. Don’t get upset if it takes a while—just keep going. Using this technique I normally fall asleep in 2-7 minutes.
When you’re anxious about something, it’s really hard to stop thinking about it and it would be better to write it down, thinking it through before sleeping.

How Can I Fall Asleep Faster?