The best and easiest way to season your cast iron skillet is to bake it. First of all, you need to clean it with mild dish soap and let it dry completely while preheating your oven to 350 degrees F. Prepare a baking sheet by placing foil or parchment paper on it. While you wait, spread vegetable oil, oleo, or canola oil inside and out using a folded paper towel. Do not use olive oil or butter. Then, put the frying pan upside down on the cooking sheet and bake for one hour. Repeat as needed.