The biggest key to delicous gravy is delicious stock, which can be made waaaay ahead of time and frozen. Use this recipe as a template for just about any kind of stock-- chicken, beef, pork, even fish. Just remember: the thicker the bones, the longer you should cook the stock.
Preheat oven to 450°F. Place some turkey parts on a rimmed baking sheet (if you are butchering your holiday turkey ahead of time, you're all set. If not, maybe buy about 5 pounds of wings, necks and/or backs-- ask your butcher if there are any spare parts you can buy). Lightly salt the meat on the bones, and roast — flipping over the pieces halfway through — about 45 minutes until they are golden brown. Remember: bones add body to the stock, meat and (a little ) fat add flavor (you don't too much fat because then the stock is greasy, but you can save a little of the fat that you drain off to make the roux later).
Traditional vegetables for classic French stock are called "mirepoix"-- Onions, celery and carrots. You should have (roughly) 3:1 bones to vegetables by weight, and 2 parts onion to 1 part celery and carrot. Precision isn't necessary though-- the stock police will not come and take you away if you add too many carrots. So while the bones roast, chop up some onions, celery, and carrots. Make sure you peel the carrots (the peels add bitterness), but onion skins add color. Oh, but don't use red onions, they turn the stock kind of a weird grayish color. Don't go buy fennel just for stock, but if you have some in your fridge, the long stalks that protrude from the bulb make EXCELLENT stock veg-- maybe substitute it for the celery-- or in addition to it. Grab a bunch of parsley stems (leaves get slimy, disintegrate and lose flavor... and they have more precious uses anyway) and thyme, a bay leaf, and some peppercorns. Not traditional, but I like to add a couple cloves of garlic, and if I have some other stems handy I throw them in too (basil, sage, rosemary or marjoram are all delicious... rosemary is pretty strong, though, so only add one or two sprigs so it doesn't overpower other flavors). Depending on what you are seasoning your roasted turkey with, you may also want to add a couple of those flavors to "echo" them in the gravy-- a teaspoon or two of coriander or mustard seeds or cumin? Some orange or lemon peel?
Once the turkey parts have roasted to a lusciously deep golden brown, take them out. This brown crust is like 99% of the flavor, and it’s going to give your stock (and eventually your gravy) amazing flavor. Put the turkey parts in a heavy stock pot, then pour off most of the grease from the pan (if you want extra turkey flavor in your gravy, save this fat for later).
Pour about a cup of white wine or dry vermouth onto the roasting pan while it’s still very hot. Using a wooden spoon, scrape up all the brown crusty bits-- this is called deglazing. Pour the liquid from the pan into the pot with the turkey. Note: (if the roasting pan has cooled off too much, you can put the baking sheet directly on your stove, turn the burner on medium, and move the baking sheet around on the heating element with the liquid to help scrape up the bits).
Add your vegetables, herbs and spices to the pot, and add enough cold water to cover the contents of the pot by 2 inches. Heat until it simmers, then let it simmer VERY gently for about five hours. Do not let it boil, if you can help it-- that can make your stock cloudy, and a little "muddy" flavored.
When it’s done, strain the stock through a fine mesh sieve. Let it cool to room temperature on your counter, then put in your fridge or freezer.