The only alcohol I drink is vodka and what I do is I drink the same amount of chocolate milk as I do alcohol and I have yet to get a hangover ever. Apparently alcohol dehidrates you so drinking other liquids helps in the prevention of hangover. Probably some unnecessary calorie intake though.

Also, stop drinking when you are drunk. This seems so simple, but people are apparently unable to grasp this concept and usually end up puking all over the place and then passing out in the bathroom and then they wonder why they don't feel so good in the morning.

Oh another tip to prevent hangovers: Don't drink alcohol.