Not Cathe, obviously - but I'll jump in -
I've been teaching for six years, and I always feel I can get better. Practice, practice, practice, and whatever you do, make sure you love what you're teaching. I've said no to teaching things that don't float my boat anymore. Not worth the pain and frustration.
Also, find an instructor you'd like to emulate. I have a couple at my gym (and cathe;-) ) who have been teaching for 20 years. Of course, they draw crowds of 60+, but they've been doing it forever! I grab ideas from them, but I also make sure to be myself in class. Connect with your class by knowing you are truly enjoying it, be real, stay focused, and remember you can't please everyone.
Remember different participants require diff. levels of attention. Advance exercisers just want to push, push, push, while the beginners might need you to slow down. Again, you can't please everyone, but as your experience increases, you'll be able to balance both ends. It's an art; remember, just make sure you love the class type, and your class will feed off that!
Cheers!