Most important step is cleaning the surface of any loose rust - which it sounds like you plan to do. Then it is a good idea to use a product like Navel Jelly that converts any remaining red rust to a tightly adhered black oxide deposit (you can find numerous products in paint departments. Then use a good primer like Rustoleum, and finish with a compatible surface coat - it will then last a long time. I prefer spray, as it gies a nice, even coat. I used this method on old metal fence posts outside, and they looked good for a long time.