Peter has got it just about right. When it comes to instructors, most of them are just dreaming of the airline job and you are the means to that end however a fair few do a good professional job.
The ones you have to look out for are those who will drop you towards the end of the course as soon as a new student walks through the door, a lot of these guys have a tendency to not let you fly the aircraft very much and like showing you how good they are, so if they fly the aircraft for anything other than demonstrating technique or aircraft safety or to off load you when they are explaining something you are with the wrong guy.
The best people to fly with are current or retired professional pilots, they are not at the club for the hours or the money, they just want to continue flying and pass on their vast experience.
I was lucky to be of an age that the guys who taught me to fly had flown Hurricanes, Mosquitos, Lancaster's, Viscounts, Tridents, VC10's and yet were more than happy to try to help put right my appalling landings in the PA38.
The final thing is that the two worst taught subjects at PPL level are aerodynamics and aircraft technical, I don't know what to recommend about aerodynamics apart from getting a copy of Kermode's book on the subject. Most of the technical teaching is stuck in the era of the Tiger Moth and so totally outdated and the only way around this one it to talk to the guys who maintain the aircraft.