Wash the area with car soap and water
Dry the area completely
Remove loose rust and paint with sandpaper or a wire brush
Sand the spot until clean bare metal is exposed
Wipe the area with wax and grease remover or rubbing alcohol
Apply rust converter if needed
Apply body filler if there are small pits or dents
Sand the repaired area smooth
Apply self-etching primer
Let the primer dry fully
Sand the primer lightly with fine-grit sandpaper
Apply matching touch-up paint in thin coats
Let each coat dry before applying the next
Apply clear coat if the paint system requires it
Let the area cure fully
Polish the repaired spot if needed
Wax the area after curing
Check the spot regularly for returning rust