Are you asking how to prepare a fresh fan for mount or are you asking how to clean dust off one that has been mounted for some time?
To prepare one for mount, I use a sharp small knife to trim away every bit of meat I can and still leave just enough to hold the feathers together. There is a knob of bone which I use a coping saw to trim away flat. Then I rub borax into the remaining flesh. I place the fan on a flat piece of wood and spread the feathers as I want them, I usually do a full half moon but have done partial spreads also and they look good. Use long finish nails under the center and behind feathers to hold the fan as you want it. Don't put nails directly thru feather quills or thru meat, just create a frame that holds the feathers arranged. Pile borax on the exposed meat and allow to dry a couple months. The remaining meat will cure like hard jerky. Afterwards, take some time to preen the feathers so they all look fresh and well arranged. I'm sure you have seen how you can pull a feather apart and then stick it back together. While you have been waiting, secure a mounting board of your liking. I prefer to use a round model made by Van Dyke's Taxidermy Supply. Follow the instructions included with your board.
As to keeping the dust cleaned off a mount, I have had good luck with these light weight dust picker upper rags made by pledge and other cleaning supply companies. Hold the fan upside down and gently brush each feather from quill to end.
