Keep the enlarger baseboard clean. I also use a Swifer duster.

http://www.google.com/products/catal...=0CJUBEPICMAY#

Using canned air is bad for the environment and only blows dust everywhere. Capturing dust is a better way. I keep my duster in a clean drawer. A quick wipe with the Swifer on both sides of the glass and your contact neg will really help.