Remove all bedding and pillows from the bed if necessary. Cover the mattress with a dropcloth.
Mix 1/3 cup of trisodium phosphate with 1 gallon of water in a bucket. Dip a scrub brush in the mixture and scrub down the canopy bed. Wipe the metal dry with old, clean towels.
Walk around the iron bed and look for areas of rust. If you find rusty areas, scrub them down with a wire brush. Wipe down brushed areas with a lint-free cloth.
Press a piece of 100-grit sandpaper onto the bottom of an electric sander and run it across the surface area of the bed frame. Repeat with a piece of 220-grit sandpaper to allow the new finish to penetrate the metal.
Wipe down the bed frame with a tack cloth to remove the sanding dust. Dip a 3-inch nylon brush into metal primer and cover the bed frame with a light coat. Allow it four full hours to dry.
Dip the paintbrush into the paint color of your choice. You can pick a shade that matches the iron color, such as charcoal or steel gray, or pick a brighter, bolder color like teal or cherry. Coat the bed in a light, even coat of paint. Allow it to dry overnight, then apply a second coat.