How to become a better mastering engineer in 30 minutes or less

One word. Move.

Nothing clears the ears and reboots the mind like a brisk walk or run. In fact, I would venture to say that a day in the mastering room is akin to an athletic event, and benefits from the same kind of preparation. Exercise, diet, and rest all play a role in achieving the state of relaxed focus needed to consistently do great work.