This article is from the Macintosh hardware FAQ, by Elliotte Rusty Harold elharo@shock.njit.edu with numerous contributions by others.
First turn off the monitor. Spray a small amount of Windex or any
other common glass cleaner onto a paper towel, NOT directly onto
the screen. Then wipe the paper towel over the screen. Finally
wipe the screen clean with a dry paper towel.
 
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