One of my favorite quotes is from Harvey Penick, author of The Little Red Book. Harvey was a teaching professional his entire life and worked with the likes of Ben Crenshaw, Tom Kite and hundreds of other professionals and amateurs. I admire his common sense approach to teaching and it's simplicity. He said, " Lessons are not to take the place of practice, but to make practice worthwhile."
In my opinion this is exactly what the purpose of a golf lesson should be. So that afterwards the student understands what he or she is to work on during their practice time. They are now ingraining a correct movement or action rather that further ingraining a poor one.
Simplicity and communication are the two traits of an excellent teacher. I work on only one thing at a time during a lesson with a student. I make sure I have communicated with the student in a manner that they clearly understand not only the movement, but also the purpose of the action.
The student has a more enjoyable experience and improves faster. This is what the art of teaching is all about.