Preheat your pan before preparing your meal. Water droplets should sizzle, then roll and hop around the pan, when dropped onto the heated surface. If the water disappears immediately after being dropped, the pan is too hot. If water only rests and bubbles in the pan, it is not quite hot enough. NOTE: Do not pour large amounts of cold liquid into your hot skillet. This can cause the cast iron to break. Never forget your potholders! Cast iron pan handles get HOT when cooking!
There is a trick to maintaining cast iron cookware and that trick is known as "seasoning" or "curing." Your food will never stick to the bottom of the skillet or pot and the iron will not rust if it is properly seasoned. Plus the cast-iron cookware cleans up easily as well. Seasoning or curing cast iron means filling the pores and voids in the metal with grease of some sort, which subsequently gets cooked in. This provides a smooth, nonstick surface on both the inside and outside of the piece.
NOTE: All new (not old pots) cast-iron pots and skillets have a protective coating on them, which must be removed. American companies use a special food-safe wax; imports are covered with a water-soluble shellac. In either case, scrub the item with a stainless steel scouring pads (steel wool), using soap and the hottest tap water you can stand.
If the pan was not seasoned properly or a portion of the seasoning wore off and food sticks to the surface or there is rust, then it should be properly cleaned and re-seasoned. Seasoning a cast iron pan is a natural way of creating non-stick cookware. And, like you cook and clean the modern non-stick cookware with special care to avoid scratching the surface, your cast iron cookware wants some special attention too.