The Book has an excellent tutorial for a simplified approach. Plus, if you get the full version of the DVD set, it comes with an iPod-compatible version to take with you and show the rider.
With the Book approach, there is no need to be concerned about pointing toes or otherwise attempting to control the board in three dimensions. All that is required is:
1. Straight arms.
2. Allowing the legs to be folded by the water pressure, driving heels to butt and knees to chest.
3. Allowing the upper body to be brought forward enough to be rolled up onto the board... but not over it.
It's basically the crouching part of preparing for a deadlift. The problem is that all three motions are counter-intuitive for someone who is encountering a new, thrilling/frightening experience. The instinctive response is to push away and counter the rope's pull.
You can spot a failure in #1 by direct observation. If the person manages to get barely out of the water with bent arms, the effect will be significant instability, forward/backward or to the side.
Failure in #2 or #3 will have a visible symptom of a wall of wash in front of the rider, followed by letting go of the rope. Many people will deny even making these mistakes. Occasionally I grab a fender (as a marker in case I get left behind), jump in the water with the rider and observe from the side. Then I can point out what's going wrong, with denials being harder to make.
Mistake #3 (upper body) is a problem for anyone with a lower back issue or a big belly. In fact, the only complete failures to get out of the water that I have observed in the last couple of years were from guys with both issues -- especially the big bellies. It's a problem that does not seem to occur to people who learned while thin and then put on weight. Anyway, taking someone who's already got some girth, making it worse by wrapping a floatation vest around the midsection, and then instructing a "bend over" action is a challenge.