Depends how deep it is? If you can catch it with your finger nail the chances are it's too deep to polish out. Try Megs Scratchx or similar but don't overdo it. Otherwise it's carefully applying paint. Take your time, build up the coats and then flatten back with an abrasive polish. Finally, apply clearcoat and a good coat of wax.
I've got one on my passenger door and am following the same process but it's a bit too cold at present to do a top job
