To keep grilled burgers from drying out, be careful not to overhandle the meat before cooking. If you add seasonings to the ground beef, gently mix them in with two forks just until combined. Then shape into 4-inch round patties about 1/2 inch thick (beef plumps when it cooks). Hamburgers are best cooked over medium heat. To test the heat level of your charcoal grill, hold your hand about 4 inches above the coals. If you can keep it there for 4 to 5 seconds, the grill’s heat is medium. Also, avoid flattening the burgers with your spatula as they cook. You’ll press out the juices that make burgers moist.