1. let the grill get hot 2. rub with something to clean old grit 3. rub again with a chunk of fat (from the meat) for flavor
The "something" in step #2 has varied over the years. Back in the day, my grandpa used to use old newspapers... which of course we know today it's not such a great idea, heh. Onions, half a potato, a corn stalk, even a chunk of brick will do the trick. You just want to make sure you don't have old chunks of stuff clinging from the grill.