The start to any good chicken gravy is a good stock.
I make my own chicken stock. I keep chicken bones, skin, and othe scraps in a gallon ziplock bag in the freezer. When I run out of my previous batch of stock, I'll make some more with the chicken scraps, a quartered onion, a few celery stalks, some garlic, etc. I'm not to crazy about using carrots in my chicken stock, so I leave those out. I get this to a simmer, skim off the foamy junk (impurities), and cover the pot, then simmer it overnight. In the morning, I strain out the scraps, reduce the stock by half, chill it, then freeze the stock in ice cube trays. I'll then store those in gallon ziplock bags in the deep freezer. I usually get 2 - 2 1/2 bags of ice cubes of chicken stock from a batch.
Then the process starts all over again.
I usually make gravy when I roast a chicken. I roast my chickens in a 12" cast iron skillet. Once it's done, I remove the chicken to a large plate or platter. I caramelize the drippings to a nice dark brown color. Then I pour off as much of the chicken fat as I can. After that, I deglaze the pan with my home-made chicken stock, using a ratio of two ice cubes of stock to 1 c of water. I usually make about a pint of gravy. Stir the liquid in the pan, scraping up all the browned drippings and allowing them to dissolve into the stock, adding color and extra flavor. Once that's done, I strain the sauce into a smaller pan. Thicken with some cornstarch mixed with water (usually a couple tablespoons each), then check the seasoning. I'll add salt and pepper as needed. My family loves it.
If I'm making a chicken gravy, and didn't roast a chicken, I'll just use a little stronger ratio of ice cubes to water, say, three cubes of stock to 1 cup of water. I'll season it with thyme, sage, onion powder, garlic powder, ground dried celery flakes, paprika, salt, and ground black pepper. Thicken and use.
KFC used to have the best chicken gravy in the world, back before the good Colonel was bought out. I have no idea what the recipe was, but I do know it involved making cracklings from either chicken fat and/or chicken skin. The resulting grease was incorporated into the gravy.