Remember plants accumulate dust as much as any other surface in your home. Clean plant leaves, especially succulent plants, with a damp cloth and cold water.Have you ever done this? The other day I was at the dentist's office when I noticed the Sansevierias near the elevators. They were filthy. Reaching for the tissue in my pocket, and checking to make sure no-one was watching, I proceeded to clean every one of those leaves.
Oh...and by succulents, I don't think they mean to include most cacti!