To prevent rust and extend the life of a cast iron skillet, it’s best not to use soap to clean it. Instead, use a about a tablespoon of coarse salt to scrub the pan after a meal.
The salt breaks up bits of stuck food and residue on the skillet. Then you can toss the dirty salt in the trash, rinse the pan with hot water and dry it with a clean towel. To further protect a cast iron skillet, rub a few drops of vegetable oil over the entire cooking surface.