Clean the door. Spray an all purpose de-greaser on the door and wipe it off with a clean rag.
Remove or apply painters tape to the hardware of the door. The door hardware includes the door knob, lock and hinges.
Repair the door as needed. Use automotive filler that is made for metal to fill in dents on the door. Fill the dent, let dry, and then sand the door smooth. Clean away the sanding dust with a damp rag.
Prime the door with oil based primer. Apply the primer to the door with a foam roller. Allow the door time to dry per manufacturers instructions.
Paint the door. Choose a paint color that complements your home’s exterior. Roll the paint onto the door with a foam paint roller. Use a paintbrush to reach difficult areas on the door. Wait for the first coat of paint to dry and then paint the door again. Let the door paint dry for several hours before use. Remove painters tape on the door's hardware, or if you removed these pieces, reattach them.