I have broken in more drivers over the years than I can count. By far the most important aspect is the new driver must understand he has alot to learn and be willing to take feedback - the good, bad and ugly. I'm happy to work with any driver, no matter the level, who is willing to learn. There is no substitute for time in the seat and being comfortable in that particular boat. Some boats are just way easier to drive than others.
If the driver thinks he is doing awesome while running over boat guides and no clue what is happening on the other end of the rope, its a lost cause. Save yourself the frustration.
For the skier, you need to keep all feedback positive and encourage the proper things to do differently. Run easy passes until the driver gets comfortable with whatever pass or how you happen to pull the boat around., Both of my kids started driving for me when they were 10, BUT they had spent alot of time driving tricks, then driving each other and mom for slalom before they drove for me. I ran lots of 28s and only shortened when I thought they were ready.
If your new driver happens to be your wife, forget all of the above and just say "you are doing great dear".