How Do I Clean My MacBook Pro Screen?
Best practices for cleaning your MacBook Pro screen suggest that you should first completely shut down your Mac, unplug it from the power adapter, and take out the battery. Once you've done that, put a little water on a lint-free cloth or paper and wipe the screen. Make sure the cloth or paper is clean and very soft.
Many stores sell screen cleaner, but it's an unnecessary expense - water is sufficient. And if you do have a cleaner of some kind, do not spray it on the screen.