Make sure they play styles you are interested in learning. Ill never forget how horrid my first teacher was. He wasn't a bad guy by any means, really cool dude but we had no chemistry. He was very into old bluegrass stuff and I was only 13 at the time so I wasn't in to anything like that and I didn't really enjoy lessons from him. So, I would advise making sure you guys have common music interests.
Hello u6s68, well, there are so many things involved with playing the guitar that I guess you need to have an idea of what you want from playing it...when I started, just like Fallenoath was saying, I didnt have the best teacher, not that he was not good, but today I see that we did not go over many important points...so you only want to play for friends or you want to be a fast player or you want to learn theory or even about guitar circuits...think about what it is that you want then you can talk about it with your teacher...if you see it wont happen look for sone else whos more in tune with your goals...hope this helps