Talking versus Drilling
I often think the most difficult part of coaching is finding that line between coaching (i.e. explaining things demonstrating techniques) and drilling (i.e. letting the student work on a skill). The more you talk and demonstrate, the more information you convey. On the other hand, the more you actually have the student drill, the more the techniques get ingrained. Where's the balance?
It really depends on the student. Younger players often are not particularly interested in a coach who blathers on and on, even if the blather is laden with nuggets of gold. They just want to play. Older students often look for more info, because they have a longer attention span, they understand the value of the info, and because they probably need the rest break anyway.
Ideally the coach says as little as is necessary for the student to get the technique right. But it's not that simple. Let's say you're teaching a kid to forehand loop. He starts out going crosscourt over and over. Then he gets the bright idea of looping down the line, and does so awkwardly. So you show him how to rotate the shoulders back so he can loop down the line more easily. Then he points out that he likes his way better since the opponent can't see it coming. And so you show him how to loop deceptively down the line by lining up the shoulders to go crosscourt, and at the last second rotating them back to go down the line. Next thing you know you are talking about the various placements when looping from the wide forehand (down the line, to the opponent's elbow/crossover point, crosscourt to the corner, extreme crosscourt outside the corner), and then you're talking about when to loop soft, medium, or hard, and pretty soon you're pretty much teaching a graduate seminar on looping to a fourth grader. (The preceding is a rough synopsis of an actual experience.)