Preheat oven to 400°F. Rub a thin layer of vegetable oil or canola oil into the cast iron skillet using a paper towel or kitchen towel. Place it upside down in the preheat oven, and place a large sheet pan underneath to catch any drips. Bake for 1 hour, then turn the oven off and let the pan cool in the oven. After it cools, the pan is seasoned and ready to use.