You are able to buy special stuff and special cloths to clean them but i say thats a waste of money. Firstly, what type of LCD do you have? The type with the matte finish, or the type with glass on the top?
If you have the type with the matte finish use a soft damp cloth to wipe away grime but dont push to hard as it will damage the screen. Wipe away the water with a dry soft cloth.
If you have the type with the glass finish you still cant use stuff like windex as the glass usually has some sort of coatings on it so use the method shown above but you are able to put a little more elbow greese into it as you are not actually touching the LCD panel, you are actually touching the glass.