Scrub the skillet with steel wool or a stiff brush and hot water
Use coarse salt as an abrasive if needed
Add a small amount of dish soap if the rust is stubborn
Rinse thoroughly
Dry immediately with a towel
Heat the skillet on the stove to remove all moisture
Apply a thin layer of cooking oil to the entire skillet
Wipe off any excess oil
Bake the skillet upside down in the oven at 450 to 500°F for about 1 hour
Let it cool in the oven
Repeat oiling and baking if needed
Store in a dry place