It seems every area here is covered, I'd just like to add(if it's not already here)is to watch how your potential instructor conducts himself, in regards to safety(would you feel safe), look over his equipment as best you can to get a feel for how he's handled his own gear. If his gear isn't at least well kept and in good condition/order, that might be a sign of how he handles things. If his equipment seems in good working order, and he has no difficulty with his own planes, then you have potential there.
I'm not saying instructors have or need top of the line gear(ask me how I know), but how they've handled there own gear is clear sign of how they might handle yours. Most of our equipment will last years(literally) when given the proper care and maintence. Your instructor should teach this also. The first step is keeping everything in good working order, without that, what good is anything. Ask this....Does he preflight his planes, and yours? Does he communicate with others at the flightline?, Are the rules of the flying site followed? You can usually get a copy of them, or they are posted. This could tell you something.
He should be thorough in my opinion, each flight starts on the ground. A good instructor will talk to you through the whole flight, as far as what he's doing, what the plane's doing, etc.. communicating in other words.
Remember too, have fun, you should be offered challenges, not beyond your abilities, but after short time, he will know what you can do, even if you don't. He should do this in a fun and easy manner.
Your entering into a very cool hobby/sport, patience is key in it. Keep coming back here, there's probably all total, over 50,000 years of experience between everyone registered on the site, you've come to the right place.