Headlight restoration projects known to me never rendered long-lasted results - mainly due to the fact that they involved removal of the factory transparent protective coat which protects the plastic headlights material both from abrasion and from UV rays. Without protection, beautifully polished headlights start noticeably fading again in one year or so. And putting transparent protective coat on the freshly-polished headlights often resulted in this coat peeling off soon.

If I remember correctly, in one of his videos Scotty suggested a good solution for the UV-related fading - to cover the plastic, after polishing, with some sort of UV-protective liquid. However this liquid (if I am not mistaken) only protects from UV and does not render any noticeable mechanical protection; neither does it allow to avoid the actual headlights polishing procedure, which requires hardware and skill. This liquid is also not available in my part of the world.

So I want to share the method I have developed myself, which (this method) - as the years have proven - actually renders long-lasting results, and has multiple benefits:
1) it does not require any polishing at all (!);
2) it creates a resilient potentially better-than-new protective coat.
Headlights restored acc. to this procedure have shown no noticeable degradation within 5 years.

So let´s begin:

Get yourself some sandpaper in different grit sizes - from, say, 800 to 2000: e.g. 800, 1000, 1500, 2000. Also get a can of clear and high-gloss transparent spray coat - it should be the best you can get, it should be well-compatible with plastic. PU-based maybe, but not necessarily.

Do the sanding work on your faded headlights, starting with the lower grit paper and working your way up to the 2000 one. There are plenty of guides on how to do headlights sanding right, so I will not cover the sanding topic here. The goal of your sanding is to completely remove both the factory protective coat and all the defects existent on the headlights surface. The result shall be a perfect non-transparent milky-white surface. Clean it, wash it, and let it dry thoroughly.

Then, use the spray can to give this surface a transparent protective coat. Yes, just like that, without any polishing procedure. The sanded surface will take care of the perfect bond between itself and the coat, and the coat will fill out all the gaps and valleys of the sanded surface microstructure, and will give you a perfectly transparent glass-like final surface. It looks like a little miracle, when the sanded surface turns into transparent glass virtually by itself, with no polish, just after it has received a clear spray coat…

Make sure the protective coat is not too thick - otherwise there will be a risk of microbubbles building up in the coat material. If you did your sanding job right, and if you gave the sanded surface a thin but even spray coating, the resulting surface, after the coat hardens, will not require any additional improvement: it will look like new fully transparent glass; no trace of the after-sanding milkyness.

If your spray coating skills are not perfect, you can always sand the imperfections (dust, bubbles etc) away, and give this thing another spray coat later. Or you can do multi-layered coating for improved protection - just do not forget to sand the surface you are coating: never ever coat glossy surfaces… You also may want to give the final surface some additional polish as well, but - if your spray-coating results were good, such additional polish will be totally superfluous.

Like I said: this method is easy, fast, inexpensive, no polishing needed - just sanding and spraycoating; and the results can last for many years. For how many - this largely depends on the quality of the spray coat material. My headlights lasted for 5 years already after such treatment, and do not show any signs of fading.