Wrestle that bag of giblets out of the turkey and pry the neck out of the other end.(Take the giblets out of the bag...I know if don't say that, someone will leave them in the bag to cook!). Put them in a big pan with about 6-8 cups of water and sprinkle with a little salt and pepper to taste. Toss in some onion and celery chunks if you want to add flavor, and simmer them, covered, until the larger pieces of the giblets can be easily pierced with a fork.
Chop the giblets into small pieces (small enough that the children won't know what they're eating!) and cut the meat off the neck. Set the meat aside.
Heat the broth from the giblets and add any drippings and juice from the pan you roasted the turkey in. The idea here is to get as much gravy as you can, while adding as little water as possible!
While the broth is heating, stir the cornstarch into the cold water until it dissolves as much as possible.
When the broth is boiling, gradually pour in the cornstarch mixture while stirring. You should see the broth beginning to thicken. Don't let it boil over, turn the heat down a little, but keep it pretty hot. Stop pouring and stirring and check the thickness. I usually use all the initial mixture of cornstarch and end up making more and adding it. It depends upon how much broth I have to work with.
When the gravy is starting to thicken, add the meat, salt and pepper, and the Kitchen Bouquet. This is a liquid seasoning that adds flavor and color to the gravy. If you've never used it, it's worth looking for, and it's worth the cost. Be very careful not to use too much, though, because it can make your gravy bitter. NEVER measure it over the gravy (THIS is the voice of experience! :) ) In a pinch, a few drops of Worcestershire Sauce will make a fairly adequate substitute, but it's not nearly as good!
The final step is to let it simmer a few minutes, and taste it again. See if you're satisfied with the amount of salt and pepper and if it's thick enough to suit you. You can always thin it with broth or water, or you can bring it back to a boil and add more of the cornstarch mixture if it's too thin.
HANDY HINT: Once my gravy is perfect, I put in a Crock-Pot on low. It stays hot and perfect throughout the meal. I can just refill the gravy boats with hot gravy as they're needed.