Smoke a joint 2 to 3 hours before you want to sleep.
Good idea, but i have also been known to use this method to wake up in the morning
If that don't work knock back a valium or 2 with a can of bourbon and goodnight see ya tomorrow.
Note: not a good idea to mix alcohol with pharmaceuticals but it does the trick, also if you need to do this more than once a week seek another safer option.