You’re almost ready to cook your steaks but—ew!—somebody left you a dirty barbecue. Quick, before you pre-heat, grab some aluminum foil. Tear off a sheet large enough to cover the entire grilling surface. Tuck it loosely overtop, shiny-side down, with a gap around the edges of the foil. Turn on the barbecue: thanks to the foil, the heat is concentrated on the grates, but the gap allows some of it to escape. (This is important. You don’t want the grates to get too hot—that could warp or damage them.)
Prepare a bowl of water. Wait five minutes—and no more than 10—and remove the foil (wear oven mitts). Dip your brush in the water before scraping. The steam from the wet brush on the hot grill will help flake away the food residue. Don’t want to use a brush? Ball up the foil, and use that as you would a brush: go up and down, and in between the grates.