Having the proper amount of fat in your beef is essential. It directly affects the: tenderness, juiciness, and flavor of your burger. The key is to strike a good balance between having enough fat to develop rich flavor, but not so much it becomes excessive and greasy. This is going to range between an 18-20% fat to meat ratio.
Chuck beef tends to be the best grind for burgers because it has about 15%-20% fat. Cut from the shoulder of the animal, chuck is leaner than ground beef and still provides enough fat to add the perfect blend of juicy, beefy flavor. If you have the option between fresh or frozen meat, fresh is generally going to provide better results. While a coarse grind, straight from the butcher, is going to give the perfect sized clumps of fat and meat mix in your patties.