If your car has a cabin air filter, make sure it's new. If not, see if your vehicle ever had one to begin with and install one. I put one in my challenger from a charger, bolted right up. No challenger ever was built with one in the early years, but the space for it, heck even the replacement filter service port was manufactured right into the windshield cowl.
Use recirculated air as often as possible, and don't drive around with your windows down.
Vacuuming the carpets once a week and door sills that aren't worn to high holy will help as well.
For dash protectant, just find something that dries completely and doesn't stay semi wet. As a general rule, I've found the more of a matte finish the protectant has, the less it tends to attract and retain dust. Glossy products tend to attract a bit more dust in my experience.
