First off, portion control. For heaven's sake! Don't dollop piles of food on your plate the size of gorilla paws. Just because it all looks so good doesn't mean you can't just come back for more. If there's one universal truth about Thanksgiving it's that there are always leftovers.
Helpful tip time! Gravy. Lots of people enjoy that primordial sludge of unknown origin. And that's great. For them. But it's going to weigh you down. Consider your gravy ratio carefully before you invite gastronomic disaster. On the flip side though, gravy is an excellent cover for flavors you detest! (see Vegetables)
Next, skip the dinner rolls. Sure they're a great way to pack on those carbs you need fuel the jog you're going to guilt yourself into after those Black Friday sales. But they'll just fill you up! They may be yummy, but many a pie monger has been waylaid from his goal by these buttery monstrosities.
Turkey is traditional. And don't worry, it won't make you sleepy. Your body is too busy processing all the other amino acids it's taking in to do much with that tryptophan. Some families also make a ham, I know mine often does. And I do love the other white meat. But if you think you're going to get a face full of prune cake after having turkey and ham you are sadly mistaken my friend. Pick one! You can always pick at leftovers after dessert.
Everyone makes some form of potato. Yams are as much a tradition as turkey. And as much as people seem to love them no one eats them any other time of year. Unless you're eating at some greasy spoon in The South, I guess. Mashed potatoes are a great medium for gagging down vegetables that you venomously scorn. (see below) Go easy on the yams, son! They are syrupy and sweet, yes, but they may also numb that sweet tooth of yours. (see also, cranberries) If you overdo it on yams you're going to have to double up on the savory flavors to whet your appetite for dessert again. And that just means less space for those sapid servings to come.
Vegetables: The bane of childhood dinners. Admit it. Kid or adult, there are some veggies you just can't stomach. They make your palate retch like a teenage girl trying to lose a size to fit into her prom dress. But you've got to eat them. If you're at the kid's table your mom won't let you anywhere near that sumptuous repast if you don't clear your plate. If you're an adult you'll be subjected to a more mature ridicule in the form of guilt. You really want to be the reason your mother-in-law cries at night because she think her cooking wasn't up to your standards? Okay, maybe you do, but your wife won't let you get away with it. So man up! I don't care if you have to go Fear Factor on those brussel sprouts, you pretend they're shark eyeballs if you have to! Gravy will disguise the taste of all but the most pungent of vegetables, but judge with caution lest ye be trapped in a black hole of gravy's design! However, I find it's best to mix them in with your mashed potatoes and chew like you're eating balut.
There you have it. The Yellow Brick Road to the Thanksgiving dessert table. Happy gorging!