I second cpal's "don't be afraid to admit you don't know".
You have to establish yourself as a credible source to your students if you want them to get the most out of learning from you. I had several instructors (and bosses) that tried to BS around an answer they didn't know. I then had to second guess everything they taught and always weigh in the back of my mind that I may have been taught wrong. Nothing is more frustrating than having to forget what what you have been taught, and remember to remember the new infromation.... if it is in fact correct.....or is it??
I have always had more respect for someone who said they didn't know. The idea is to actually pursue and attain excellence, not just convince me you have achieved it. By admitting you don't know it will force you to learn it, which will help ratchet you up to the next caliber.
