Use a stiff wire brush to remove any loose rust.
Wearing rubber gloves, scrub around the frame with a nonabrasive scouring pad dipped in kerosene or a commercial aluminum brightener. Take care to keep the liquid off straps and webbing, as it could stain them.
Rinse the frame with warm water, and dry well with a cloth rag.
To help prevent corrosion and add shine, you can wipe on a very light coat of car wax with a cloth rag.
Scrub off any loose paint or rust with a stiff wire brush.
Abrade the entire surface of the piece with 180-grit aluminum-oxide sandpaper. This will provide a better surface for the paint to stick to.
Cover the area under the piece with a drop cloth. If you're planning to use a spray paint, make sure that all nearby areas-- particularly walls and plantings--are also covered.
Apply a metal primer, either the brush-on or spray variety; let dry.
Brush or spray on the new enamel paint; let dry. If you are making a drastic change in color, or if it is recommended on the label, apply a second coat.