In looking for a good instructor I would definately have some good questions for them. How long have they been teaching; how many students do they currently have; How long have their students been with them; What is their background in music; Just some basic questions. If they get upset because you are asking, then they are probably not who you want to take lessons with. Ask if they include Music Theory as part of their curriculum. Ask for references. Usually the references is going to tell you a lot about the instructor. And of course your local music store is your starting point when looking for an instructor. Either they will have an instructor there or they can point you in the right direction and also tell you possibly instructors to stay away from. Good luck.