Whenever I'm stressed I try and do things that will take my mind off of it. Work out, go for a run, drive around town, play some video games, anything that will make you forget about your stress.
I also agree with the above comment on getting into a relaxed state before bed, as strange as it sounds, warm milk also works for me. Just put milk in the microwave for 10 seconds and drink it. Either that or tea, just make sure to check that the tea isn't caffeinated.