A car's surface is made from metal covered with a primer, base colour and clear topcoat. Car scratches occur when an object strikes the surface of the car. If the scratch reaches through the surface of the paint, you can remove or minimise it at home by sanding down the surrounding paint to even out the scratch.
Wash the scratched area with car shampoo or soap and warm water, then dry the area completely with a towel. Since you're actually not removing the scratch but rather sanding down the car's paint to even out the scratched area, you have to be careful to not sand too deep. Select shoe polish in a colour that will stand out against the paint shade; for instance, choose black shoe polish for repairing a scratch on a white car. This will ensure you don't accidentally sand out the paint underneath the scratch. Smooth the shoe polish carefully over the entire scratch, making sure not to extend past the scratch.
Select ultra-fine wet/dry sandpaper with a high grit (such as 2000) from an auto parts store. Standard sandpaper from a hardware store with a low grit is rougher and will remove too much paint. Fill a large bowl with cold water and two drops of liquid dish soap, then dip your sandpaper into the bowl. According to Popular Mechanics Magazine, the water will help the sandpaper cut into the paint surface more effectively. Start at one length of the shoe polished-covered area and sand gently with small strokes, at a 60-degree angle rather than a straight up and down motion. Rinse the sandpaper after every four to five strokes. Lightly sand the area just until the shoe polish is completely removed.
Dry the entire sanded area thoroughly. Apply a small amount of rubbing compound (about 1 tbsp) to a terry wash cloth. Rubbing compound can be found at most auto parts stores and can be used to safely buff car surfaces at home. Buff the area where the scratch was removed. Gently wipe the surface with your terry wash cloth, using circular motions. Buff the area until the area is smooth and no residue remains. Wash the area with car shampoo or warm water if buffing doesn't completely clean the area, then dry the area thoroughly. Apply a quarter-sized amount of car wax to a soft cloth and smooth onto the area in a circular motion to seal the surface of the paint. If the scratch is still visible, it may be too deep to remove at home and could require professional care.