Experience is the best teacher in this case, as it is in so many cases. Until you have had to scramble to find an answer to a student-generated question not covered in the text, you don't really know how to teach grammar. My PG training was almost entirely conceptual and theoretical. Even as I speak in class, I can think up numerous counter-examples or anomalous situations that don't quite fit that pat formula I just delivered. This has made me favor non-explicit teaching of structure, which can be controversial or unpopular.
Responses are anonymous, and in no particular order.
These are great questions and I'm glad someone is finally asking them. Recent MA grads know English grammar, but they are not taught how to explain how to use it to ESL students. This is the biggest deficiency I see in MA programs nationwide. But they don't know how to use the language. If MA grads are studying TESL to become teachers, then their MA program has to do a better job of preparing them to actually teach.