To season a cast-iron skillet, first scrub it with a stiff brush in warm, soapy water.
Rinse the skillet, and dry it completely.
Spread a thin coat of olive oil or melted vegetable shortening to the entire surface, both inside and out. If the skillet has a lid, spread the shortening on the inside and outside of the lid as well.
Line the lower oven rack with aluminum foil to catch any drippings. Preheat the oven to 375 degrees. Place the skillet upside down on the upper oven rack, and bake for 1 hour.
Turn the oven off, and let the skillet cool completely before removing it from the oven.
Repeat the greasing and baking procedure two or three more times. The finished product will be dark and have a nice sheen.