Wash the affected area thoroughly with soap and water
Dry the area completely
Remove loose rust, paint, and debris with sandpaper, a wire brush, or a grinding tool
Sand the surrounding area to smooth the edges
Apply a rust converter to any remaining rust
Clean the surface with wax and grease remover or rubbing alcohol
Mask off nearby areas you do not want to paint
Apply body filler if there are pits or small holes
Sand the filler smooth after it cures
Apply a rust-inhibiting primer
Let the primer dry fully
Apply matching automotive paint in thin coats
Apply clear coat if needed
Let the paint cure according to the product instructions
Wax the repaired area after full curing
Inspect for remaining rust and repeat treatment if needed
Replace the panel if the rust is severe or the metal is perforated