I would recomend wet sanding with ultra fine sandpaper like a 2000 or finer grit and polishing with a medium rubbing compound,preferably machine polishing.
Once you eliminate the scratches,move to a finer polish,and finish with a good glaze like Meguiers.
Depending on the color of the paint(use extreme caution when sandin metallic colors)you should be able to make it look like new.