When I take them out of the box for the first time, they get a spritzing of The Treatment Final Detail spray wax/cleaner. Then, if they are Exoto, GMP, Minichamps or selected AutoArt, they go into their own plastic display case (usually AutoArt) and they don't get dusty. For my other cars that don't get to live in a clear box, I have a large soft makeup brush that I use to dust the hard to reach places. A can of air (mentioned in previous posts) also works well.
I give all my cars a good coat of wax when they come out of the box. I do some detail painting and use bare metal foil, especially on muscle cars, to detail the chrome window and wheel opening moldings. I use a large soft artist brush for cleaning dust from them as it will reach small areas but won't damage small details like wiper blades, etc.