Techniques for removing the paint from a vehicle will somewhat differ depending on how much paint you need to remove. When deciding which method of paint removal you need, it is always good to do your research. Are you trying to remove some graffiti from a car? Or are you trying to repair a scratch or dent on the car? We will cover some of the common types of auto paint removal here, but it far from a complete list. If you decide to use a commercial product to remove the car's paint, always make sure you read and follow the manufacturer’s instructions.
Maybe your car was parked too close to a house that was getting painted, or you see some scrape marks on your bumper that look like paint transfer. If you are simply trying to remove some over-spray or light scuff marks from a car without damaging the paint itself then it might be best to start with a cleaning wax. This is often ideal as it means that you wouldn’t need to use anything abrasive or deal with potentially dangerous chemicals - just some elbow grease and a microfiber cloth. If that ends up not being enough you can look into a buffing or rubbing compound, or possibly a clay bar. These would be more abrasive and need to be used with care. You may have to wax and buff it again afterwards just to mitigate the effects of the compound.
Some commercial graffiti removers or other chemicals such as thinner or acetone are popular remedies for removing spray paint from a car's exterior. Keep in mind that some of these chemicals can also damage or remove the surrounding paint. This means that there is the possibility of making things worse if you are not careful. It is probably best to try to test any chemicals on a section of paint that you would not normally see. Be sure to thoroughly wash the vehicle afterwards to remove any remaining chemicals.
In the case of removing the car paint during the course of other bodywork, there is the option of a chemical paint stripper, but this is usually only for use in extreme cases. It may damage things other than the paint itself and it’s usually not necessary to remove that much paint. It can also be tricky to handle and there can be the potential for injury when you’re using some of the more aggressive products out there.
Most body repair shops would use sandpaper of varying grits in order to smooth out and flare any scratches. If you are trying to remove a lot of material, such as would be the case if you need to take it back down to bare metal, you will want to use a coarse sandpaper to start with and if you need it to be smoother you can always jump up to a finer grit sandpaper. There is also a technique known as wet sanding where you use water (or some other liquid) while sanding with finer grit paper. This helps to prevent the sandpaper from clogging and allows particles to be washed away instead of becoming trapped under the sandpaper which can cause additional scratches.