Use Mothers Plastic Polish
...with a foam polishing pad.
Followed by Plexus Plastic Protectant
...with a Microfiber Glass/Plastic Cleaning Cloth.
absolutely no problems with my 2001 Toyota Celica headlamps
Using A foam polishing pad with Mothers Plastic Polish, go over the lens repeatedly in both a left-to-right and up and down pattern. The foam is slightly contoured. As you approach the edges of the lens, work with just the edge of the pad. This gives you a crisp edge to avoid hitting surrounding paintwork.
Continue polishing until the lens is polish free. Wipe the lens with the Fiber Microfiber Glass/Plastic Cleaning Cloth and inspect the lens. If you feel the transparency can still be improved, repeat the polishing process.
After polishing, spray the lens with Plexus Plastic Protectant and wipe with the Fiber Microfiber Cloth.
Plexus Plastic Protectant contains a UV inhibitor to retard UV induced discoloration. Every time you wash the vehicle, spray the plastic lens covers with Plexus to prevent further discoloration.
Notes: UV induced discoloration does permeate through the plastic over time. The key is early treatment. While most of the cloudiness is on the surface, severely discolored lenses can not be brought back to optical perfection.
[edited to add directions/guide]