hangovers are caused by dehydration and hypoglycemia from the buildup of byproduct from the breakdown of ethanol. drink lots of water before bed, drink lots of water when you have a hangover. all you have to do is replenish your bodys supply of liquids. in the experience of my friends (since i dont get hangovers), if youre drinking liquor, its roughly one glass of water per shot of liquor. i dont know what that equates to with beer. natural sugars in juices can help as well, in moderation.
exercise will also help use up some of the NADH builtup from ethanol breakdown. sooner you get rid of it, the sooner you can reduce the nausea, since being nauseated comes from the inability to continue breaking down the ethanol.
and that "hair of the dog that bit you" nonsense (drinking more alcohol to get rid of a hangover) is a joke, not a remedy. the thought is that if you get drunk, you wont feel hung over.