A direct-view TV can be cleaned with a paper towel and glass cleaner unless it has an anti-glare or other coating. If so, or if you are unsure, use a damp cotton cloth so you do not scratch the coating.
Rear-projection sets with screen shields--all microdisplays and some CRTs--should be cleaned with a dry or damp cloth, and with a mild soap if they are particularly dirty. If the screen streaks, buff in a circle with a dry cloth. Never use paper products, which can scratch the screen.
Any rear-projection TV without a screen shield needs a special cleaner and rag, which you can buy at a TV service store.
Plasma TVs can be cleaned with a soft cloth and mild soap, if the screen is very dirty. Any heavy cleaners or paper products can strip or scratch the screen.
LCD flat-screens require very careful cleaning. Do not press too hard on the screen, don't use paper products, and don't use any sort of cleaning soaps or other mixtures. To clean, use a damp cloth, and immediately dry it with another, dry, soft cloth. Microfiber cloths often come with TV sets for cleaning.