There are many specialty acrylic cleaners on the market (Blue Ribbon Plexiglass Cleaner), but if you’re in a pinch a mild dish soap and water solution works great. Just mix one teaspoon of dish soap with one quart of water. You can pour this mixture over the glass or put it in a spray bottle. Allowing the solution to run down the surface of the glass actually helps pick up excess dirt and particles. Use a lint free, nonabrasive cloth like microfiber,terry cloth, or cotton flannel. Only wipe where the plexiglass is wet- never use a dry cloth on dry plexiglass.