How to efficiently wash my garage?

Hey, not actually my garage, I'm at my parents house and I have 2 days before they come back. I would like to advance them a bit before they arrive homes and start the cleaning of the garage (we had people in winter putting all their gear here and stuff to rework the house) The picture is the ground after I passed the broom, there is a ffffick layer of dust, and.im wondering the best way to get rid of a maximum