I boarded an A330 in 17 minutes once as we were massively late on a turnaround.
We put crew checking the boarding cards OUTside on the bridgeto tell pax to go left our right before they got to the door. So effectively had 2 at a time going through the door. Suppose that trick wouldn't work on any small planes.
Also told crew in cabin to be proactive and politely hustle people into their seats!!