I have a very light canister vac that I can carry around on a shoulder strap, so I used that, with the bristle brush attachment. That worked very well. I also used a dry cloth over larger wall areas. I tried to work from the top down (tops of doors and windows first, etc). It took forever (I'm still finding spots I missed, and it's been several weeks). I hope you have help!

I agree with duckee. The first step is to get as much of the dust into a vacuum cleaner as you can. Use the brush attachment. If you have a vacuum cleaner that uses bags, vacuum once, change the bag, and vacuum the walls again.