As has already been mentioned, simply respecting his time and reacting to what he has to say as far as flight instructions should be enough for most Instructors.

I had a student this Saturday that I had taken on several flights and then told them I was going to take a couple of flights with my plane. Their response was "well, that's OK, my batteries are charging anyway. They'll be ready in about 15 minutes. We'll go back up then, right?". The response was "First off, I was telling you, not asking you. I'll let you know when I'm ready for you again". Some people see instruction as a right and are not cognizant of the fact that we are volunteersdonating our time.