Being a Band Director, I am a member of the group "Band Directors". There is a lot of different topics and helpful tips from veterans in the field. You have to be approved for admission to the group.
Another group that is beneficial is Google Classroom for Music Teachers. Ideas and strategies that will help teachers create and implement assignments and activities using Google Classroom. I also teach a Technology course that I utilize Google Classroom for as well, so it's a good information source for that application.