Thanksgiving guests of America tomorrow you will honor the important tradition of uniting Williamsburg artists and Upper East Side financiers, Mets fans and Yankees fans, and new wives and ex-wives, over a day of float-filled parades, football games turkeys, turduckens, or vegan Tofurkys. In 24 hours, in your rental car, on the Metro-North train, or in a taxi uptown you will make your way to your Thanksgiving Day host’s front door. If your host is anything like my grandfather-in-law immediately you’ll be asked: “Would you like some red wine with tonic water?” To which you say, “Of course I would!” Once my grandfather-in-law mistakenly grabbed salad dressing instead of tonic water. Cheers?

In the seldom-used living room, you’ll be greeted by a sea of unfamiliar faces — and there’s no use trying to keep their names straight. It’s Thanksgiving, and you’ve crossed that invisible threshold again. You’re no longer a second-grade teacher or a marketing guru; you’re The Guest.

And as The Guest, you might know the ropes and ease into the familiarity of your hosts’ rescue dog, Rocco, opening the garage door by pawing the clicker, or admiring Grandpa Joe’s use of “the bread napkin” to mop sauce from his beard. Congratulations, you’ve got a leg up; you’ve been invited to this Thanksgiving celebration before — so, relax and hit the turkey hard.

However, if tomorrow is your first holiday with a new family (because you’ve met a new lover, friend, co-worker, or schoolmate), and you’re ignorant of the house rules, I’ll share with you what I’ve learned from repeated dining with my own family of traditionalists and eccentrics, the Hatzopoulos Clan:

The conversation focuses on who died in the past year and who is terminally ill. One cousin is always so late. We call his cell phone, and when he doesn’t answer, we’re torn between serving the meal and calling the police.

Some plates are hand-dried, other platters are air-dried, and only some of the stemware is dishwasher safe. It’s an unspoken logic, so I politely clear the table and defer to the experts.

Of course, as The Guest you want to blend effortlessly into the family camaraderie. After all, all you want is to make the cut! And get invited back next year! But be wary. You can make yourself too comfortable in someone else’s home.

Last year, my brother introduced a tall Swedish woman to our Thanksgiving table. He had met her the night before and thought she was “fun.” She was missing a few teeth, talked loudly, and drank beer continuously. She wowed us with a story about driving to California and discovering a drug lab. She “loved horses” and the “new BMW 3 Series.”

Over dessert, she announced that she was spending the night because she had fallen ill with “the poison” in her stomach. This was not in reference to the food we had just fed her, we assumed, but an eccentric, Swedish way of saying “the stomach flu.” My husband, a board-certified internist, wasn’t sure what “the poison” meant exactly, but urged her to drink some water and rest. Invitation to Thanksgiving 2007: Denied.

So, Thanksgiving Guest, you are set with the difficult task of making it effortless for your host to throw his or her best Thanksgiving ever while still leaving your stamp on the event. A great dessert, a tear-jerking story about Habitat for Humanity, a killer Dr. Phil impersonation — whatever it takes so that come Thanksgiving 2008, you’re on the list. Whether you accept the invitation, of course, will be up to you.

Ms. Koutas Poch is the author of “I (Heart) My In-Laws” (Owl).