Don't drink heavily. Many times hangovers are caused by lack of hydration, so drinking water during the time you are drinking can help prevent the hangover symptoms. If you are able and have no contraindication to it's use, Ibuprofen can help with the headache part. If abdominal pain occurrs or excessive vomiting a more serious condition could be present and should be evaluated.
Don't drink! Most believe that the symptoms of a hangover is the result of a person being dehydrated. Thus, drinking as much water---yes, plain water, as you can before going to bed has been the most successful way to prevent a hangover. As for getting rid one, sorry to say that we still don't have a good answer. Tylenol (acetaminophen) and lots of fluids are as good as any. Save your $ buying herbal pills. They don't work.