Skip the Harsh Cleaners: You Can Remove Rust with a Potato! The potato trick is so handy (and non-toxic!) and it isn& limited to cast iron ? you can use it to remove rust from baking pans, knives, and other household tools. Tips from The Kitchn
Excellent guide to using and caring for cast iron cookware with pictures. Make sure to read the comments at the bottom where he explains an easier way to get rid of rust by putting the pan in a campfire to burn off rust.