I started with some 600 grit sand paper making sure to evenly sand the entire surface of the lens and worked my way up to 2500 grit in five stages. After that was done, I used a Porter Cable random orbital buffer/polisher with different backing pads and compounds to get the headlights polished. While I had the lights out of the car, I also replaced the plastic adjusters inside the lenses. Over time these can fail from all the heat cycling they experience.
The end result was a night and day different from where they started and for a few hours of work it was rewarding and certainly better than spending the money on a new OEM set of headlights.