Mayor gave perfect instruction for making pan gravy. I would only add that if you are going to make a large batch, you can season the gravy. For instance, if you are making sausage gravy, the main flavor componants of pork breadfast sausage are salt, sage, sugar, cayenne, and black pepper. Just a smidgeon of the cayene is needed. Add a little bit of the other seasonings, let cook for about four miutes and taste. Add more of the seasonings to get the flavor you want. Be careful with the sugar as it's easy to make the gravy too sweet.
If you are making a beef gravy, add onion, garlic, MSG (optional), salt and pepper to enrich the flavor. A1 sauce and Lee & Perrins Worcestershire Sauce are great additions to a beef gravy. You can also play with various flavors of liquid smoke, fennel seed, oregano, sweet basil, hot sauces, or pre-packaged season packets such as Washington's Deep Brown sauce (great product), soup bases, boullion, etc.
Don't be afraid to season a gravy or sauce. you can add curry spices, even melt cheese into a gravy (don't let this come to a boil whle melting the cheese or it will clump).
Be creative. Have fun with your sauces. Learn to make a proper Bechemel, and the derivitive sauces from it.
Seeeeeya; Goodweed of the North