Before you head to the party sit down and have a snack. Eating a full meal might make you feel uncomfortable, but a quick snack can rectify that. Have a piece of toast with jelly, a handful of nuts or a piece of fruit. Having anything in your stomach can keep you from overeating once you get to your party.
As soon as you arrive at the party and get past the introductions and hellos, work your way over to the bar or cooler and get a glass of something low in calories like a diet soda. If there's alcohol served pick something like a gin and tonic or a light beer, which has lower calories than any of the other drinks. If you do drink alcohol, alternate between alcoholic drinks and non-alcoholic drinks. For example have a gin and tonic, then grab a glass of water or a diet soda. Just make sure you keep something in your hand all night. When one hand is occupied, you're less likely to reach for snacks to keep yourself busy.
Then spend some time looking over the food options, before you start loading your plate. It's easy to start loading up your plate with fatty foods before you see everything they have on the table. If your host is serving fresh, steamed or grilled vegetables fill your plate with those first. Only after you've eaten those should you go back for a second helping. More than likely you'll already start to feel full before you get to the fatty foods.
While you're at the party, position yourself away from the buffet or food choices. How many times have you found yourself reaching for the chip bowl just because it's there? You grab a handful of chips while talking with friends and before you know it, the whole bowl is empty. The further away from the food you are, the less likely you'll be snatching up those calorie rich foods.
When the deserts start calling your name, make smart choices. You might think you'll satisfy yourself with a few pieces of candy, only to find yourself pigging out on the cake later. If your brain keeps begging for cake, go ahead and have a small piece or split a regular size piece with a friend. Don't think you can fool your body into accepting three apple slices when all it really wants is that ooey gooey chocolate cake.
The best way you can control yourself at a party is to bring along a dish of your own creation. This is especially helpful if you're not sure what food your hosts will be serving. Whip up one of your favorite low fat recipes and take it along. Not only will your host be happy for the help, but you're ensured of having at least one thing you love that's good for you.