When you purchase a new barbeque they come with grills made of stainless steel, porcelain or cast-iron. Stainless steel and porcelain are slightly easier to maintain, but in my opinion nothing beats a traditional black metal cast-iron grill. If you purchased a cast-iron grill you will want to take some preventative measures to make sure your grill lasts a long time and doesn't rust. The steps you are about to follow are called seasoning your grill.
When you first get your grill, wash the grill with warm soapy water and then dry it with paper towels. Make sure you don't let it drip dry as we want to make sure we've removed all moisture. Next take a paper towel and some vegetable oil (I use olive oil), and coat your grill with a light coat of oil. The oil adds a protective layer to the grill as well as prevents food from sticking to it.
After you've coated your cast-iron grill, place it back inside your barbeque and heat your barbeque up on medium temperature and allow the grill to heat up for 20-30 minutes. You have officially seasoned your grill!
If you used your barbeque prior to seasoning don't lose too much sleep over it, because it is never too late to do it. Seasoning your grill after having used it for awhile unseasoned is better than never seasoning it all and will go a long way to increase the life of your grill.
Another thing you should make sure you do immediately after you have finished cooking, is to take a wire brush designed for barbeques and clean off any carbon debris left from your food. You should do this while the grill is still hot as it makes removing the excess carbon significantly easier.
Another quick tip, although it isn't 100% necessary is each time prior to cooking, I take some PAM aerosol olive oil and spray it over the areas on the grill that look a little dry. Make sure you have the burners off when doing this or you could catch yourself on fire! Again, spraying the oil on the grill will not only help prevent your grill from rusting, it will also make your food stick less to the grill resulting in much nicer grill lines!