Cleaning monitor screen

If it is nano-texture glass, see: How to clean the nano-texture glass on your Apple display - Apple Support

Otherwise, see the following from How to clean your Apple products - Apple Support

To clean the display on your iMac, dampen the cloth that came with your iMac—or another clean, soft, lint-free cloth—with water only, and then wipe the screen. 

The regular, glossy glass screens can be cleaned with pretty much any glass cleaning product, but I got the best results with a bit of rubbing alcohol and a clean cloth. This does not apply to the nano-texture glass, or to MacBooks.