The first thing we were taught in my nursing degree pharmacology module was the physiology of a hangover. My lecturer swore by 2 pints of water, a banana and 400mg of Ibuprofen (so long as you are able to tolerate it) before you go to bed along with 1g Vitamin C.
Always worked for us although I think most of us over 30 will agree that the older you get, the longer and more painful the hangover until in the end it isn't worth it except for special occasions!