Gravy too thin? Simmer it until reduced; or thicken with a little arrowroot or cornstarch that's been dissolved in cold water, then whisked into the boiling sauce.

Too thick? Thin with water or stock.

Lumpy? Put it through a fine strainer.

No taste? Use salt and pepper, soy sauce, more pan drippings, chicken stock, or port, Madeira or bourbon.

Looks muddy, not glossy? Add cold stock or water, simmer, then skim often.

Unthickened gravy or jus didn't emulsify? Skim off almost all the fat, then add more stock, boil hard to emulsify. If the fat is still separating, take it off the heat, whisk in 1 tablespoon heavy cream or cold butter for every 1 cup gravy.