I find that taking echinecea helps shorten the lengths of my cold/flu. I prefer the liquid drops (usually you can find it in a natural food/health food store) over pill form, even though the taste is disgusting.
Definitely up your intake of vitamin c--eat more fruit as Katie suggested, and also drink plenty of water.
Also, take it easy, and try to keep the temperature in your bedroom at a moderate temperature when you sleep, not too cold. Hot showers with lots of steam helps clear up congestion. Wash your hands before you eat and keep your hands away from your face (jeez, I sound like a germ-phobe, but being sick really sucks).