I think this can be not emphasized enough. I keep a spray bottle handy to keep the headlight wet when sanding by hand. The water moves away the old particles. If you are using an orbital tool or a drill I kept a hose flowing on the headlight to keep it cool. It's very easy to overspeed to the tool and melt the plastic. The other problem with using orbital tools is sometimes the sandpaper edge will catch and scratch the lens. I would stick to hand sanding unless you have old headlights to practice on.