Blow your baby
Blow the majority of the light dust from the car with a fine compressed air blower/gun, or a portable shop blower. We have a great little one that is battery powered from Milwaukee tools. It's always used before we even touch the cars. If the car is very dusty, it's good to do this outside, then move the car indoors. If it's not possible to do this, you will need to gently sweep or vacuum the light dust now from the floor, otherwise it can blow back onto the car as you walk around cleaning them. It gets annoying having this happen after they are clean.