A terrific book for teachers is Teach Like a Champion: 49 Techniques that Put Students on the Path to College by Doug Lemov.
Lemov, who is managing director of Uncommon Schools (a charter school program), spent a lot of time observing master teachers to see what techniques they use. He's collected 49 techniques and describes them in detail in this book. He also includes a DVD, referenced throughout, which shows examples of teachers using the techniques, incredibly important to understand (and eventually being able to apply) the techniques yourself.
There is a lot about classroom management, an area that is so incredibly challenging for new teachers--and without it, not a lot of learning can take place.
But there's much more as well, ways to drive excellence in your classroom.
Much of this can be fairly easily adapted to the choral situation, but what would be great (and a great doctoral topic) would be to follow through in observing and filming choral master teachers with a view towards these techniques (or new ones) to see how they're applied.
You could also build a great course for soon-to-be student teachers around this book.
Don't think it's only for K-12 (even though that's its stated level) there's much for the college/university teacher or leader of community or church choirs as well. The principles don't change!