Answer #1: Making sure that they are dry
before you put them away, a light layer of cooking oil will protect them if your
kitchen is a bit damp. -- DK Comment
Answer #2: Rust is good for you, well the tiny amount of iron leaching in to your food will probably be improving your iron levels. Some years back a medical journal published an article about how in India (at the time) the iron cooking vessels supplied significant amounts of iron that was a useful supplement to the vegetarian diet. I have also read a paper (based on a scientific study) that showed that leaching from aluminum cooking utensils were a problem in India. So stick to your tin coated iron muffin tins. I do not bake myself, but suggest that you ensure that your tins are dried well before storage and that you take the advice of the previous contributer and coat them with a food grade oil. -- ed at qznaz Comment
Answer #3: Rust Removal from Baking Tins. Just watched a video on cleaning rusty baking tins; The presenter warned about the dire consequences from consuming rust, she also used Baking Powder before rubbing the rust away with steel wool. The poisoning bit is rubbish and the baking soda is unlikely to have an effect, however the steel wool bit is going to work, but fine emery paper is probably a bit better. -- ed at qznaz Comment