An excellent article on keeping your knives in order by Chad Ward.
Cast iron pans should be black and glossy due to a protective layer of carbonised oil coating the steel. When oil is heated in cast iron, it bonds with the metal through polymerization, creating a seasoned layer. If the pan starts to turn grey or flaky, you need to season the pan again. If the pan has rust, first gently scrub with water and some salt, then dry thoroughly in an oven. Wipe the pan with cooking oil and put in an oven upside down at the smoke point for the oil (for light olive oil this is 240’C) for an hour.
Do not cook with lots of sugar or tomatoes for prolonged periods of time as it can affect the oil coating.
Do not leave food to stand in cast iron pans. Clean immediately after cooking, don’t soak for long periods of time. Dry after washing. Wipe with a drop of oil if the surface looks dull before storing.
Scrub with steel wool and scouring powder, rinse and dry it. Heat for a minute or two until the bottom is too hot for your hand. Rub with a paper towel and oil and let it stand overnight. Sprinkle a teaspoon of salt in the pan, heat again, and rub vigorously for a moment with paper towels, rub pan clean.