The easiest way is not to clean it at all. Seriously, more damage is done by people trying to clean their optics than by any dust or dirt on them. Cleaning a telescope's mirror is something which should be done only every five to ten years, and then only if it is really really dirty. Dust has absolutely no effect on the performance of a telescope, unless it's really heavy.

When you _really_ need to clean your mirror, in at least five years from now, this is how to do it. You need to remove the mirror cell from the tube, and then remove the mirror from the cell. Blow any loose dust off with a blower brush, NOT canned air. Rinse under running water. If that isn't enough, immerse in a mixture of distilled water and isopropyl alcohol, with a few drops of liquid dishwasher detergent added. Use surgical cotton (not cotton balls, as they're abrasive) to _gently_ swab the surface, using no more pressure than the weight of the cotton. Rinse with more of the water-alcohol mixture and stand on edge to dry. Remove any droplets with the tip of a paper towel.