For cleaning them, just make sure any chemicals/cleaners are designed for use on vinyl. Glass window cleaners are not.
Always use a soft cloth. Mild soapy water works great. A little bit of liquid dish soap is fine.
Things like pledge or novus, or any number of things like that are NOT cleaners. They may be useful, but they don't clean. They either polish, or just fill in the little scratches. They should be used in addition to cleaning, and like anything you sand or grind, you shouldn't polish anything as often as you clean it.
Your windows however may be past the point of just cleaning (in other words, it may be the case that even if you clean them, they simply need to be polished to make them less hazy).
If that's the case, I highly recommend the the Novus 3 step process. If you use it properly, it can transform your windows from hazy to almost new again!
https://www.amazon.com/dp/B002UCYRZU/?tag=wranglerorg-20