As with most foods, we'd always recommend trying to prepare your gravy at home, which means you're able to control what goes into it.
Homemade gravy is typically made by taking the drippings from a roasting pan (i.e. the browned juices and fat from your meat) and adding cornstarch / flour and water until the sauce thickens into a gravy.
While homemade gravy would be ideal, sometimes this isn't always possible, and gravy granules are the next best option.
Shop-bought gravy granules can often contain added sugar, so be sure to check the ingredients list for this.