Separate the cooking fat from the pan juices—a gravy / fat separator makes this job easy.
Heat the cooking fat (or butter) over medium-low heat until melted. Carefully whisk in the flour to help avoid clumps. Cook until the mixture darkens in color, about 1 to 2 minutes. This step is called making a roux.
Whisk in the pan juices (or broth/stock) and bring to a light boil. Cook while whisking occasionally until the gravy reduces and thickens. Season with salt and pepper and serve warm over meat or potatoes.
Homemade chicken stock (which is what we typically use) contains much less salt than store-bought broth. Whichever you use, remember to taste test as you add salt to your gravy.