I was on a boat the other day with a really nice suite of electronics; fish-finder, standalone radar, two multi function displays and a half dozen or so engine gauges. Everything was neatly installed but all of the screens were really hard to see. Turns out that the owner of the boat had been diligent about keeping up with the cleaning but had been doing more harm than good as he had been cleaning the screens on the electronics with Windex. Windex in common with many cleaners of this type has high ammonia content and this is the very worst thing that you can use on your screens as it makes them go cloudy and/or milky.
Read the instructions that come with your equipment when it comes to cleaning, almost all say that the best thing is a little water and a clean microfiber cloth. No fancy chemicals required. Distilled water is best as it is free of impurities. For clean spot free shine just spritz the screen with a little water and wipe carefully with a clean microfiber cloth. I have a small pump action bottle in a drawer close to the nav station as shown above specially for this very purpose – two or three ounces of water lasts a whole season.