I probably should have reversed the order of the first two items, because you can't really think about your menu until you've determined who you will be inviting and how many people you will have to serve. Decide whether you will send formal invitations or just call everyone. I host Thanksgiving every year and don't send invitations out, I just call people to let them know "Yes, I am hosting Thanksgiving again this year"
In my case, I'm going to need to make sure I have enough food for 28 people. I'm assuming my husband's grandmother, parents, siblings and their families, and niece and her family will be joining us, plus 4 possible unknown others. My father-in-law doesn't eat Turkey, so I make ham and turkey every year. My favorite dish is the Brandied Candied Sweet Potatoes, so while I could probably do with just the mashed potatoes each year, I make both. I do divide the mashed potatoes in half though, and leave half plain and use the other half to make Creamy Garlic Mashed Potatoes. So, 3 kinds of potatoes. We are in the Midwest, meat and potatoes country. At this point I could probably leave off everything else and at least half the people coming would be fine with it.
I'm probably going to make two kinds of Green Bean Casserole this year. First, the mushroom soup, french fried onions, green bean type that everyone knows. Second, I want to try a new recipe that will hopefully taste just as good, but have a lot less sodium and preservatives, maybe. I'll let you know how they go over.
I make my own cranberry sauce every year, but after the first year I also include a can of the jellied cranberries in a can. Most of them won't even try the homemade sauce, the few that did really like it. I keep making it because I like it.
Don't forget to think about drinks and dessert.
Wine, coffee and hot buttered rum for the adults. Punch and hot apple cider for the kids. I'll probably have ginger ale as well for those that have to have soda, and Diet Pepsi for my father-in-law.
I always make Pecan and Pumpkin Pies, this year I'm including Blueberry (my mother-in-law and one brother-in-law's favorite), and Apple (I have a ton of them). I also make something more along a cake/cookie/bar type item that the kids might like better than pie. I'm still deciding on this. I'll pick something out and post the recipe tomorrow.
I'll make my grocery list later today, I write down everything that I need for each recipe. Then consolidate the amounts and check the pantry to see what I need. If you need fresh herbs, try to get them early and freeze them if possibly. Finding fresh Thyme or Sage the weekend before Thanksgiving is all but impossible! And they won't last long in your fridge. I'll have tips for freezing herbs a little later this month.