NEVER use soap, bleach or scouring pads on your cast iron, or overheat it while dry and empty, and you won't have to re-season it.
Just wipe out anything left in the pot or pan with a paper towel and put it away.
If food gets stuck on it, heat it up and clean it with salt and a rag.
If something is REALLY stuck on it; put it on the stove with a little water and scrape it out with a metal spatula to get the really difficult stuff
out, then use salt as above, then wipe it down with Crisco or cooking oil for good measure (you don't have to, but you can put it in the
oven @ 250 F for a few minutes).
Be sure your cast iron is completely dry before you put it away. If your oven or stovetop is still hot, drying it with just the residual heat is fine.
This will keep it from rusting. By the way, if it does get some rust on it don't fret, just wipe it out and wipe some Crisco or cooking oil on it
and bake it in the oven at 250F for 15 minutes or so. The rust won't hurt you it'll just add a little iron to your diet. The rust on the cast iron
cookware is not corrosive so it's not going to eat a hole through it; it just doesn't look as pretty.