Everybody has their own way of cleaning a mirror. I try a dry method first, but you have to follow the instructions as far as using a 100% camel hair brush, and VERY light strokes. This only works for dust, not stuck on crud. You can see exactly how I do this on one of the pages at my web site, which is as follows if you are interested in trying this method at all:
http://home.comcast.net/~astrohammer/tips.htm