I use a garbage bag and spread it in/over the sink flat (as in, one side is up and the other is down.)

Then i can pick it up by the corners and a shake or two above the garbage gets most of the hair. Fold it up so i open it the right way up next time and its golden.

Ill upgrade eventually by getting one of those plastic-barber-like-bibs and throwing some suction cups on one end. They stick to the mirror over the sink and the other side would tie around my neck making for less hair spread, and easier cleaning and use than a garbage bag.