[xyg]

I would say these aspects are important:

An instructor's understanding of the topic he or she is teaching. It is hard to describe but the vision and the depth are just different. In some occasions, I find that it is my preparation prevents me from fully understanding what the instructors are seeing.

An instructor's passion for the topic, which brings moments for learners to feel "this is fascinating /amazing /cool /interesting. I have never thought about that". It seems that passion cannot be faked or manipulated, which means one cannot be prepared to demonstrate passion when teaching a course.

Teaching and presentation skills, can be trained.

Visualization and other technicals, can always be improved.