One of my earliest mentors in training gave me many immensely valuable pieces of advice. And two that I've learned to ignore. I was thinking about this today while re-reading an old classic, Teacher as Servant: A Parable, by Robert K. Greenleaf (now out of print, but available used). So, here are two bits of advice I learned to ignore.
1. "Always perpetuate the illusion that in the classroom, you are God."
By that, I'm sure he meant to say that one must establish and maintain credibility. Once credibility is lost in a class, you seldom have the chance to regain it with that group. It's also important to maintain the authority that keeps you in control of the classroom process. But I've found it more useful to consider myself a servant of the group than its master. Yes, it's my job to maintain control; but only because they're paying me to do it, and because it serves their best interests for me to do so.
As usual, there are exceptions to every rule. I had one class that consisted entirely of highly-paid business consultants. I was told up front by their manager that it was a smart-alecky group that would give me trouble unless tightly managed. So I went in with the Top Gun approach, very authoritarian, but at the same time letting them know that "You're the best - but we're going to make you better."
2. "When you are doing class introductions, try to identify up front who the troublemakers are."
I tried this exactly once. And I got what I expected: troublemakers. I haven't done it since. Now I expect up front that everyone in class is going to have fun, learn a lot, and contribute. It doesn't always happen that way, of course, but I think my expectations and mindset help it to happen more than it otherwise would.
The night before a class, as I'm falling asleep, I repeat to myself the affirmation (in present tense), "This is the best class I've ever had."