Wash with hot soapy water/scrub out. Rub inside outside with canola/other oil. Place on cookie sheet! in oven 250 degrees for 2 hours. Take out, wipe out with paper towel, place on low heat burner for 1 minute.
I only cook in cast iron. I even have some of my grandmother's pieces and use them! This is a good guide to using and seasoning cast iron. I do not use soapy water unless I HAVE to and I use coconut oil from Traditions to season mine