DON'T! Ordinary tap water often include chemicals like chloride that will leave a residue on your screen.
Coarse paper towels or cloths may even scratch and damage your very sensitive LCD display, causing clouding and can even lead to dead pixels.
How to clean an LCD screen:
1. Unplug or turn off your LCD screen or device and closely examine the condition of the screen.
2. Take notice of any smudges or areas to be cleaned.
3. Use a Microfiber Cloth to remove any obvious dust and gently brush off any dirt particulates.
4. Although you can clean any LCD screen with a 50/50 solution of distilled water/isopropyl alcohol, it is recommended that you acquire the proper cleaning solutions and cloths to clean your LCDs.