Find a teacher who is built like you are, or at least has similar flexibility. A teacher with similar flexibility is more likely to swing in a way that is compatible with your physical characteristics. Your height, weight, looseness-tightness, etc.is all important.
For example, I am tall, slender and loose-jointed (6 feet, 170 pounds). Learning from somebody who is short, chunky, and tight-muscled won’t do me as much good as learning from somebody built like me who has similar flexibility.
Flexibility is most important factor. Other factors can be adjusted for more easily by you and your teacher. Ask his (or her) experience teaching people similar to you.
Obviously, teaching skill and golf swing knowledge is more important than anything, but keep these other factors in mind.
Try and avoid a teacher who wants to turn every golfer into a copy of his own swing.
The best teacher for you also communicates in a way that you understand. Plain language is better than jargon.