It's very easy to sand to much(through the paint), especially on ridges. Just keep it wet while sanding. Use a block with the sand paper on flat surfaces, and your hand with no block on the ridges, contours, etc. Also, be carefull with the polishing wheel. It's easy to take to much paint off with it also. It takes practice to get good. I've done it before, but i would consider myself far from being good. I am alot better at tinting windows than paint and body work. The secret to a good paint job is the prep work. Also, lots of practice and experience. Just be sure to sniff all of the paint fumes everytime you paint(joking). I've actually heard where people can't do this for a long period of time without actually screwing up your brain. Probably not a good profession to get into.