Do...

Grab a small plate. Take one small plate, and use it to make your first pass through the buffet line. It's a well known fact that the more food you take during this first trip, the more you'll eat. Don't take a dinner plate and a salad plate, and make both plates full of food. Limiting yourself to one plate and enjoying it will help you eat less.

Mix it up. Try new foods, and make sure to grab a variety of dishes including vegetables and protein. If you focus on making a colorful plate, you probably won't grab too much of one really bad thing!

Eat slowly. If you're at a holiday, enjoy the occasion and all of the conversation and atmosphere that go along with it. After taking one plate from a buffet, make sure that you enjoy your food and finish it before you go back to grab seconds. If you eat slowly, most likely, you'll eat less and still reach a feeling of fullness.

Don't...

Go overboard on sauces and dressings. Sauces and dressings are a restaurant evil, because you never quite know the ingredients. They are often fattening, and creamy due to cream and other fatty dairy products. When adding a salad dressing or sauce to your meal, just remember to use sparingly. Use a separate container to get salad dressing so that you don't use more on your lettuce than you need to. 

Indulge in liquid calories. Feel free to stick with water for your meal! You will be able to eat more food, and water pairs well with everything. Alchohol and sodas come with a lot of extra baggage, including extra calories that aren't nearly as enjoyable as dessert. Make smart choices, and you'll get more out of a buffet!

Feel obligated to eat certain foods. If your aunt made a standout bread that she says is great with butter on top, feel free to politely decline. Your health and commitment is more important than eating something you know will set you back. If you want to taste it, take a small cut of bread just so you can say you tried it. Relatives and friends will be impressed with your devoutness to your goals!