Wash and dry the area thoroughly
Remove loose paint and rust with sandpaper, a wire brush, or a grinder
Sand until clean bare metal is exposed
Apply rust remover or rust converter if needed
Clean the surface with wax and grease remover
Apply body filler if there are pits or holes
Sand the filler smooth
Apply self-etching primer
Sand the primer lightly after it dries
Apply matching automotive paint in thin coats
Apply clear coat if needed
Let the paint cure fully
Wax the repaired area after curing
Replace severely rusted panels if the metal is too thin or perforated
Seal seams and edges to prevent future rust
Keep the car clean and dry to prevent rust from returning