Help Needed — Game Master Classes

So…I’ve promised the Talking Boys that I will give them a weekly “Moderator’s Class” in how to moderate a roleplaying game.

But…my mind is kind of blank.

So, I would be grateful for any comments y’all might have on what makes a good roleplaying game master or good storytelling in general. (Because, in truth, isn’t a Mary Sue story–a real one, not when people smear a perfectly good female character by calling her a Mary Sue–really just the written version of the Game Master’s Pet NPC?)