"Whether vintage or modern, dust your hat daily with a soft-bristled brush. Stiff bristled brushes will tear the felt. Western stores frequently sell hatter's brushes for this dusting job. Use a dark-colored brush for dark hats and a light colored brush for light hats."
Furthermore, brush your hat in a counter-clockwise direction, against the lay of the nap, so that the felt is worked well and dust is best removed. Enjoy your hat!
Black - dark bristles for dark hats.
White - light bristles for light hats.