There are a few different methods to thicken gravy, but the most common is to use flour. You can also use cornstarch, rice flour, or tapioca starch. The best way to thicken gravy is to whisk the flour into the drippings before you add any liquid. This will allow preventing lumps from forming. You can also make a slurry by whisking together equal parts of flour and water. Then, just whisk the slurry into the gravy until it reaches the desired consistency. If your gravy is too thick, you can thin it out with some additional broth or water. Another way to thicken gravy is to simmer it for a longer period of time. This will allow some of the water to disappear, leaving behind a thicker sauce. If your gravy is still too thin after simmering, you can try adding some tomato paste or pureed vegetables. These will help to add body to the gravy. Just be sure to simmer the gravy for a few minutes after you add these ingredients so that they have time to break down and thicken the sauce.