Be careful using some chemicals, such as acetone, lacquer thinner or MEK. They have a tendency to make the surface sticky.
I use a citrus based mildly abrasive hand cleaner, Such as "Go Jo". With a scotch green or white pad if bad. Then I cover them with 303 aero space protectorate to help restore the plasticizers. The fenders are all treated with 303 each year, even if they just need a little soap and water to clean.
You can get fender covers--easier on the boat, and cheaper than fenders. Some fenders carry a life time guarantee.
Filling with air--either the needle valve or some have a plug you screw out, and a taper fitting as in an air gun (no High pressure), just enough that they provide a "cushion".
Clean after each major use--or trip. Should last a long time. We found one 36" round fender which had floated over 1000 miles on The Atlantic. Since we had plenty of time on passage, we scraped off the foot or so of barnicals and marine growth. Cleaned with the hand cleaner, and used for a number of years. The surface was faded, but worked fine.