Wrought iron rusts quickly and is seldom left unfinished, so you're usually painting over an existing finish when you paint it. It's best to strip an old finish that has begun to flake off, but stripping can be difficult with wrought iron; it's usually molded into complex, hard-to-reach curves. Some refinishing experts prepare wrought iron by sandblasting it, but an alternative that's more homeowner-friendly is to power wash it. You can safely paint over the old finish if it can withstand a high-pressure blast of water. After treating the bare metal for rust, repaint by spraying or rolling and brushing.
Power wash your wrought-iron furniture with a nozzle that delivers a concentrated water pattern. Use either the red nozzle, which delivers a 0-degree spray pattern, or the yellow one, which delivers a 15-degree pattern. A concentrated spray removes more paint, and it can't harm the furniture.
Let the furniture dry completely, which should only take two or three hours on a dry day. You can also wipe it dry with a rag.
Sand all rusty areas with 150-grit wet/dry sandpaper; then treat them with a rust inhibitor. Be thorough; any rust you miss will bubble up under the new paint.
Set the piece of furniture you're going to paint on a workbench or piece of plywood suspended between two sawhorses. It's easier to see what you're doing when the piece is at eye level, and you'll get cleaner results, especially on the feet.
Prime the piece of furniture with metal primer, which also helps inhibit rust. The easiest way to prime -- and to paint -- is to spray the material, using an aerosol can. Another efficient method is to roll on the paint with a 4-inch roller and use a paintbrush to get paint into crevices.
Roll or spray on two or three coats of metal enamel. Let each coat dry for the time recommended on the container before applying the next. Let the final coat cure for 24 hours or more before using the furniture.