The mortar that holds the entire meal together, gravy is really pretty easy. There are two basic approaches: Separate the fat, cook it with flour to it to make a roux, then add back to pan juices., or use Aunt Margaret’s.
After going back and forth with mixed results both ways, I’ve settled on Aunt Margaret’s technique for (usually) fool-proof gravy. Here’s how it goes: Once the turkey is out, set the roasting pan on the stove and turn the burner (or burners, if the pan spans two) on medium high. While the juices are heating, scrape all of the dark, cooked-on goodies from the bottom and edges of the pan.
Use a small bowl and mix cold water (and it must be cold water or you get lumps) slowly into a cup or so of flour (I like to make a lot of gravy, like a couple of quarts) until it becomes a smooth, not-too-viscous paste. You want this sort of runny.
Slowly pour the flour and water into the roasting pan, stirring constantly. When the mixture is smooth, you’re ready for more liquid. I usually make a few cups of turkey stock with the neck, and I’ll add water if I need more volume, but I’ve stopped using canned chicken broth (see Ruhlman for why). Bring the gravy to a simmer and cook for awhile to thicken. You can add more of the flour/water mix if you want, but always make it separately.
If you think the gravy isn’t brown enough, add some Kitchen Bouquet, a nearly flavorless caramelized sugar solution mostly for color (Maggi liquid seasoning is the same thing). It’s not necessary, but I never make gravy without it. If you still have lumps, whisk them out or use an immersion blender.
Finally, and especially if there are any fat slicks on the surface, add a cup or two of milk or cream or creme fraiche. Let simmer until you’re ready to eat.