I just did my headlights last weekend and they look like new.
I bought a sheet of 1000 grit wetsanding paper, a sheet of 2000 grit and a headlight polishing compound they sell at any autozone.
From ugly yellow to brand new and shiny look in less than 20 min.
Wet sand them with the 1000 grit until they feel smooth, the with the 2000 grit, make sure you use circular moves and make sure you cover the whole surface. Clean and dry them to find out spots that might need more sanding. They shoud look all cloudy but feel smooth.
Then rub them with the polishing compound, apply good pressure to the surface, and clean. Repeat as many times you want to give them that perfect shine
