1. Be funny.
2. Put effort into class preparations.
3. Demonstrate your expertise (ie actually know what you're talking about).
Thinking back to my CELTA days, we had to rank a certain number of teacher characteristics from most important to least important. Then we compared our list to a list generated by CELTA students (though I wasn't sure if it was every CELTA student ever, or just ones that had studied at the Institut Britannico). Kindness was the top one, but unfortunately I can't remember the other two. I do remember, however, that I ranked "demonstrates considerable knowledge of the subject they're teaching" (or whatever) pretty high, and that was down near the bottom of the list compiled by the students. That baffled me: I don't care about nice if one teacher is a bitch who has her shit together and another is a nice guy who doesn't know what the hell's going on. This may be why my favorite teachers were almost always the ones who were universally loathed for being boring or mean: I could recognize that they knew what they were talking about. Likewise, if it was clear to me you didn't have your act together or had some serious intellectual honesty/cognitive dissonance issues, I don't care a jot if you're nice or mean or the Queen of England.
Or, as this anonymous Korean high school author put it:
That is to say, as teachers are people who give us information we didn’t know, providing more thorough explanations and showing that they are fully ready to teach us can make the students admire them.
It's interesting to see how similar my answers are to his, and how different ours are from the CELTA list.
What do you think makes a great teacher?