There are lots of things people tend to say, but pretty much all of those end up discredited. I'm sorry, but I don't think much can be done the night after.
Try drinking lots of water, taking Tylenol or something along those lines, perhaps a hot shower, & wait it off.
A few, totally accurate tips about how to avoid getting a hangover in the first place:
1) As a general rule, darker-coloured alcohol tends to cause worse hangovers than drinks of a lighter colour. (Anyone ever notice how rare bad hangovers are with Vodka?)
2) Choose a drink & stick with it the rest of the night. Don't mix different types of alcohol.
3) Did you know that Red Wine is said to cause the worst hangovers.
4) Eat when you drink.