1. Friendly and Congenial:
I think the most important characteristic of a good teacher can have is to be friendly and congenial with his students. It is a plus point for a teacher, if his students can share their problems with him, without being afraid or hesitant. I think students have always thoughts their teachers as their enemies (in a funny sense though :p). With this mentality, they can never be close to each other, and besides that how many teachers did you like who were NOT friendly, and were rather arrogant and rude?