I lay them out in the driveway, hose them down, then scrub with a pole brush from NAPA auto supply ( long, soft bristles). I use citrus based solvent cleaner not too strong, lots of scrubbing then rise and hang out on clothes lines and fences.
I quit using canvas drop cloths after a case where a student technician set a sooted up log on the drop cloth. I immediately vacuumed it up and lifted the cloth only to see a big dark spot on the very expensive white carpet. Luckily, it came out with lots of vacuuming directly. We tried blankets but you cannot spot holes in them easily the way you can with the rubberized canvas. Also, you always have the same clean side down. Some techs use black drop cloths and I've used black furniture blankets but on top of this canvas sheet. I have seen techs accidentally step into a pile of soot only to track it across the floor.
BTW, I have some friends who had their logo silk screened on their drop cloths. Their firey red socks are emblazoned" Got Flame?" so the homeowners can read their feet as they work. Yes, around Philly, you AlWAYS remove your shoes upon entering a home. No exceptions and no booties. If you don't remove them, you'll buy a few rugs whether your fault or not.