Remove any hardware attached to the metal and use painter's tape to cover any parts that don't need refinishing but can't be removed.
Wash the metal with all-purpose household cleaner or mild degreaser, such as dish soap. Rinse thoroughly and make sure it is completely dry before proceeding.
Fill in any dents and scratches using auto body filler. Sand the damaged area before filling it and add the filler so it fills just slightly above the blemish. Allow it to dry thoroughly, according to package directions, and sand it with 100-grit sandpaper.
Scrub away any rust spots using sandpaper, steel wool or a wire brush.
Sand the entire surface with 120-grit sandpaper and wipe away the dust with tack cloth.
Apply a oil-based primer that dries quickly to the entire surface. Allow it to dry completely.
Paint the surface with an acrylic paint using either a sprayer or a roller brush. Apply one coat evenly and let it dry completely before applying a second coat. You can even apply a third coat if desired.