Some tips for using sandpaper to sand auto paint are selecting the right sandpaper grit to minimize scratches and using a sanding block for slow, even strokes. Make sure to sand in all different directions, and change directions often while sanding to prevent imperfections in the car's surface.
A low grit sandpaper removes the paint from the car quickly and is best used when stripping all of the paint from the entire car. If using a low-grit sandpaper, a higher grit sandpaper may be necessary to sand out any scratches caused by the lower grit. Using a sanding block makes it more likely that any high or low spots on the car's surface are noticed.