If really bad, start with 400, then 600, 800, 1000, 1200 or 1500, finish with 2000. Then get some good ultrafine polish, and I use a 6" random orbit polisher. I like the Simonize headlight kit for the clearcoat dissolving spray and pre polish rubbing compound. When finished, either have them re clear coated, or better, apply the Laminex 20 mil vinyl overlay. it provides both impact and UV protection which is what hazes unprotected lenses. I can make a headlight look better than new.