The three little words are "I don't know." The biggest thing about a classroom that makes learning work or not work is the connection between the instructor and the students. Many of the items above relate to establishing that connection. Nothing will destroy that connection as quickly as the instructor speaking nonsense. It only takes one student in the class to know that the instructor is bs-ing, and credibility has been lost for good. And, if the instructor loses credibility, he/she has nothing. Students will tune out. AND, it is okay to not know. The instructor can not be expected to know everything. That is the nature of humans. Never pretend to know. Just say, "I don"t know," move on, and if possible try to find out before the next class and answer the question then.