I use a soft, lint free cloth and distilled water to clean it. To polish out fine scratches, use a plastic polish such as Novus 2.
I have a large picture with a plexi front. Years ago, before I knew any better, I'd clean it a couple times a year with windex and paper towles. The way they make it sound, doing that will cause bad things to happen, like start WWIII or worse. However, it still looks nice and clear to me.
On time I cleaned permanent marker off a glass window with one of those green pads made of nylon. I was not aware of the abrasives in it!
John