But I'd rather control the process: seasoning is simple, and maintaining it is even simpler. To season a new pan wash it well and dry it. Preheat the oven to 350 degrees while you warm the pan gently over low heat on top of the stove. Using a brush or a paper towel, spread a tablespoon or so of a fresh neutral oil like corn or grape seed in the pan; the surface should be evenly covered, with no excess. Put the pan in the oven, bake it for about an hour and let it cool in the oven.
That's it.
It's helpful if the first few uses of the pan involve oil, like sautéeing or deep-frying. If you care for the pan properly, it will darken with use and become increasingly smooth, beautiful and easy to cook in.
Once the pan is seasoned, routine washing can almost always be done with a scouring pad, not steel wool or anything else that will damage the seasoning (although the worst that can happen is that the pan will have to be reseasoned).
Despite many recommendations to the contrary, a little mild soap won't tear off the seasoning.
Cast iron can rust of course, but never if you dry it after washing and keep it out of rain and floods. If rust does appear, scour it off with steel wool or sandpaper, and reseason.
Cast iron really struts its stuff when you want to get a pan good and hot and keep it that way. For "grilling" a steak indoors, it can't be beat. Ridged cast-iron "grill pans" are good for two reasons: They raise the meat slightly above the surface, which promotes browning by preventing escaping liquids from contacting the meat, and they leave grill marks, which are attractive if nothing else.
Cast iron is as good at browning as any other cookware, and its mass lets it hold a steady temperature so well that it is perfect for deep- or shallow-frying.