Your pan should already have a tablespoon or so of fat in it (leftover from browning your meat); if it doesn’t, supplement with olive oil. Now add an aromatic or two to the pan: A couple of smashed garlic cloves or a sliced shallot; a sturdy fresh herb, like thyme or rosemary. Give them a few minutes over gentle heat so they release their flavors.
Source: How to Make a Simple Pan Sauce
This is essentially making a gravy for your leftovers, which is a straightforward enough idea, but I like that this recipe is so simple and quick, and you can make it straight from the pan after reheating left over food.