Two things help with this. 1) If at all possible, have the booth set up in a place that isn't very dusty. 2) Turn the booth on and let it run for a little while before painting. Hopefully any dust that is floating around gets sucked into the booth filter.
This is how I do it since I bought my booth that is similar to the one from Micro Mark. I haven't had a dust issue, but my painting skills are so bad that dust would be the least of my problems.