Jeremy Weiss has put together quite a large library of systems videos that go through D-Zone Coverage, Breakouts, Offensive Attacks, Forechecks, Regroups, Power Plays, Penalty Kills, and Faceoffs. Understanding these systems should give players a good idea of what’s underlying a lot of hockey plays.
If you’d like more drills to run, Jeremy Weiss has a pretty nice series of drills drawn on the whiteboard. A playlist including more than 75 different drills can be found here:
Theory on coaching can be a little hard to find for hockey. So much of it is really about working with people and how people learn best. One guy who does talk about it a little bit directly related to hockey is Jeremy Weiss. I don’t always agree with everything he has to say, but he puts out some nice Sound Bytes that should make you think.