Turn off the TV and disconnect the power. Make sure the screen is cool. This is more important with plasma TVs, as they throw a bit more heat than LCD TVs.
Dampen a lint-free cloth with clean water (do not use strong chemical cleaners such as alcohol, ammonia-based cleaners, or window cleaners) and wring it out until it is moist and will not drip. Chamois, microfiber, or 100 percent cotton are best. Do not use a napkin, paper towel, or tissue paper, as wood-source materials may scratch the screen. Gently wipe from the center of the screen in circles outward reaching the frame; be sure to clean the corners. Do not rub, scrub, or apply too much pressure. Wipe the case if desired. Use a dry, lint-free cloth to wipe away any moisture on the screen or the case, again using a circular motion on the screen.
You also can purchase special screenwipes, available at most computer stores. These can be used on your computer monitor too.