Prepare the cabinets by removing the inside files and washing the cabinet and drawers with soap and water. Rinse well. Make sure all the dirt is off the cabinets. Let dry.
Sand the finish of the cabinet using 80-grit sandpaper to create a rough surface. Also remove any rust. The paint will adhere to it.
Wipe surface to remove dust from sanding.
Prime the file cabinet with a spray primer made for metal. Spray slow strokes, moving from one side to the other until entire surface is covered.
Let primer dry until it's no longer sticky.
Spray paint cabinets using paint made for metal. Spray slow strokes, moving from one side to the other until the entire surface is covered.
Let paint dry overnight.
Spray another coat of paint if you see any primer coat coming through.