Always make sure the driver/observer and the skier are in sync as to what happens when they fall. This discussion happens before the skier leaves the swim step.
In my boat, if you're ok you wave your hand above your head. If you're injured you don't wave, you don't motion the boat back you don't try and move. Just lay back and we will be there at warp speed. Before we started this process, I had folks that were hurt trying to get my attention by waving the boat back to them, which implied they were OK.
Communication, communication, communication.