H2O, before, during, and after.
a hang over is your body asking for water. if your well hydrated before you start drinking, its unlikly that you'll even get a hangover. if you do, drink more water next time. once you get a hang over, its just a matter of time. not much helps, drink water, take pain killers. but dont take em right after you drink, it will cause liver damage. take em the next morning.
-AKHog