If it is pretty dull you can mix fine rubbing compound, polish, and water in a plastic bottle with a small top. mix to a somewhat runny consistency. slop some on and buff with a power buffer, but go easy and keep it moist so you don't burn the paint-or -take off too much (don't push hard), weight of the buffer and keep it moving. Only use slow speed. buffs out the dull stuff and polishes at the same time. I learned this from a detailer at an auto dealer I worked at long ago. There may be something better, just my 2 cents.