So I'm completely lost on what to do. I have no idea why my hamburger gravy for my mash potatoes is so bland. 1lb ground beef, 2tbsp worcestershire sauce, 1onion, 1/2 tbsp of garlic powder, 2cup milk, 3tbsp flour, and salt&pepper to taste.  I doubled everything except only 3cups of milk instead of 4. When actually eating it the gravy just seemed kind of bland. 
Gravy "goodness" comes from the flavor left behind when the meat cooks. All those bits & pieces left behind on the caramelized bottom of the pan is the stuff you want in your gravy. So start, by cooking the ground beef until you see "glaze" in the bottom of the pan and the meat is well-browned. Then add your onion into the beef, stirring it in and cooking a couple minutes (until the onion softens).  Meanwhile... mix equal amounts of soft butter and self-rising flour. Add this, your seasonings and ~1C of milk to the pan. Stirring until everything is well blended. Then add more milk, a half cup at a time, until you reach your desired consistancy.  If your gravy ends up too thin, don't stress, cooling the gravy down will thicken it up some. (note: if your butter is cold when you go to mix it with the flour, pop it in the microwave for 8-15 seconds. It doesn't need long to soften, so start at 8 seconds and add a couple seconds at a time until the butter is soft enough to stir into the flour.) 