To prevent your dinner from sticking, you need to clean and grease the metal grate. Doing this makes the grill more hygienic, facilitates flipping your food, and, most important, gives you impressive grill marks. Repeat the cleaning and greasing process when you're finished cooking. It's easier to clean a hot grate, and the oil helps prevent rusting.
To clean the grate, preheat the grill and, when it's hot, brush the grate with a long-handled stiff-wire grill brush. If you don't have a grill brush, use a ball of crumpled foil held in long-handled tongs.
To oil the grate, fold a paper towel into a small pad, dip it in a bowl of vegetable or olive oil, and rub it over the bars of the grate using long-handled tongs. Do this carefully to prevent oil from falling onto the coals.
You can also oil the grate with a chunk of bacon or steak fat.