How do I clean dust from a popcorn ceiling?

Vacuum is what I do.

Have you tried vacuuming it? We have an attachment to our vacuum to reach over head on the ceiling and ceiling fans etc. If you do not own one, maybe you can ask a family member or good neighbor to borrow theirs. Also, you can rent one for a day at a store rental in your area. Hope this helps. Do the tops of doors, cabinets etc when you do do it.

I use the brush attachment on my vacuum also a broom covered with a towel will work

A soft bristle brush paint brush is a good option but be prepared for it to take some time, a few sneezes as the dust floats down, and a lot of dusting and vacuuming once you are done. You won't knock down as much of the popcorn this way as long as you have a gentle touch but the dust will come off.