Have a bath, have a warm drink, wind down a bit.
don't go to bed immediately after stopping work, do something a bit mundane to get yer brain to stop working for a bit. Watch Big Brother or sort some washing.
Also, if you're tossing and turning in bed, get up, walk around the house for a bit, then go back to bed. Works for me every time!
Stop worrying about not sleeping, just appreciate the chance to have rest for a bit. The sleep will come when you are more chilled out about it!
Good luck!