Gravy is to the main course what icing is to dessert. It can hide a multitude of errors, and properly done, it makes whatever was already good even better. Turkey or dressing a tad dry? Gravy will moisten it. Mashed potatoes taste a little flat? Gravy will add some umami. Green bean casserole a little sticky? A little gravy will loosen it up.
It is hard to go wrong with a traditional Giblet Gravy, pretty much the gold standard for Thanksgiving gravy. Make a simple stock from any turkey parts you are not roasting with the bird — neck, back, tail, wingtips, heart, gizzard (but not the liver, because it will cloud the stock) — or use store-bought. Make a roux, add the stock and perhaps some pan drippings (or not if you are making it in advance). Simmer, season and serve. Find more detailed instructions here.
Good Stuff Gravy simplifies that process and tastes just as good. The ingredients are essentially the same but rather than making a roux, you make a flour and butter paste and stir it into your simmering stock.
Vegan Double Mushroom Gravy uses dried porcini powder for extra flavor and as a thickener for the mushroom or vegetable stock. No flour, no butter, no roux. And LOTS of mushroom flavor.
Savory and full of flavor, a well-made gravy will enhance any component of your Thanksgiving meal, though for dessert, use icing instead.