The most important rule is also the most obvious: stay hydrated. Having a glass of water between cocktails helps you digest the alcohol and gives you something to drink instead of booze. After your last drink, order some soda water with bitters — Angostura is fine — and a slice of lemon for flavor. There's something about the minerals in bitters that will make you feel better when you wake up. If you wait until the morning to drink some Emergen-C, you're already behind the curve. If you're planning a long night of partying, try to drink the harder stuff earlier in the evening and then switch to beer. But if your party is ending the evening with shots, stay away from sugary cordials. Even a shot of Scotch or an herbal liqueur like Chartreuse will be less likely to give you a hangover than something very sweet. Finally, try to avoid going straight to bed after a night of drinking; the longer you're able to stay up and moving around after your last drink, the better off you'll be in the morning.