So far what I've found to be the best is to neutralize it first, you can get the spray on rust neutralizer at just about any automotive store or body and paint supply. Clean the area best you can and spray the neutralizer on, it will turn black, can be sanded and painted. What I like about the neutralizer is it is an actual acid type product that does what it says, neutralizes the rust. If you just coat it with any product that doesn't have the neutralizer in it, the rust is going to come back big time. It's nasty though, you don't want to get it on your skin or breath it.
