Dust is a problem for a lot of people. There are several things that one can do to help with the dust problem. Holders can and do hold static that can attract dust. You can clean them but some think it is better to vacuum them. There is a spray that is used in the electronics industry that you can spray to help eleminate static. Vacuum the inside of the camera. That can be a large source of dust. As Brian said, run the shower for a few minutes before you load the film. The humidity will help keep the dust down. After the film is loaded maybe you could store the holders in a zip lock baggie with the zip lock zipped.

Some of these may help but keep trying different things to see what works for your system.

The dust on the drying negs is something that cleaning the area where they hang and then after they are hung up...leave and don't come back into the room until the film is dry.