I have used Novus 2 polish for over 20 years. We used it at work to keep the lenses on emergency vehicle light bars clear.
When I got my Unimog, it had a cloudy soft-plastic rear cab and side windows that you couldn't see through, so I tried the Novus on those. Turned the plastic crystal clear (which really surprised me!).
I use old (but clean) athletic socks, fluffy side out, as applicator and buffer. Shake the bottle really well, put some on the sock which is over your hand, and gently start rubbing the plastic in a circular manner. I usually work on small areas, around 6" square, at a time.
Do this until you start to get a dry layer on the plastic (a minute or so of rubbing) then use a clean sock (or a t-shirt, or other soft cloth) and gently buff the layer off. Repeat as necessary.
Be patient and gentle, don't rub the polish on too hard or fast, as this generates heat which can distort soft plastic! A buddy of mine didn't heed my warning on that and ended up with some small bulges in his M35 rear window.
There are 1 and 3 grade Novus polishes, but I've never bothered with them.
Cheers