microfiber cloth (the one you can find for glasses is ok) and if there's grease on the lens, isopropyl alcohol (can be found in pharmacy, but is becoming very difficult to get it in small quantities, at least here)
Or you can try with ethyl alcohol, but not the commercial "denaturated" one, cause the denaturant they add it, left a bad residual ..... maybe the edible type that can be fount 95 degrees, pure, clear transparent, may work.
Or can try the fluid that is used in optics shops for lens cleaning, but i'm not sure, it depend from the fluid ..... if is the type that don't left any "protective" on the lens, maybe it work
Then for the borders of the lens, you can also use the microfiber cloth bended 2 or 3 times, in the corner it made ..... or just take a piece of thin cardboard, like a ID card, cut an angle, so you obtain a small flat part in the corner, and then use it for press the microfiber when wiping the lens ..... remembering to change the part that touch the lens each wipe or two, otherwise you just redistribute the dirt that you have take away from the lens, again on it.
Anyway, never use solvents, if you're not absolutely sure that the lens is glass, and not acrylate
Edit: also if you're sure that the lens is glass, never use acetone (ketone ?) for it, when it's on the module ..... most of the time, these lenses are glued, and it unglue them, or at least melt and spread part of the glue on the lens, making the things worse ..... and in any case, if the inside expander is HT acrylate (metacrylate), the vapors are enough for opacize it, wasting the module.
