The problem with using say, a brush to remove dust is that you're rubbing the card. This generates a lot of static electricity. The IC's on printed circuit boards can die from a 5 volt static jolt. Walking across a carpet on a non-humid day can charge your body with 25000 volts.
Canned air is the safe way to go. Try not to squirt liquid into your box. I try to buy the stuff when it's on sale at Costco. Otherwise, it's a rip off.