Clean The Screen

I found that there are companies who sell special tissues so they do not damage the radiation coming from the screen. I would recommend Office Depot or any other store that sells computer related products.

My belief is to do it whenever you feel the screen is getting a bit dusty when you shut the screen off...

Are the same sprays used for all types of screens, or is there something specific for LCD and somehting different for CRT?

I've actually tested 2 brands, and both were suitable for both types. (I assume you mean desktop screen and laptop screen).

 Best would be to read the sticker on the spray ;)