The instructor is doing you a favor by training you. Treat him as such. Thank him after every training session, even the short ones where you don't get to fly as much as you wanted to. And he's there because he cares about the club's growth and new pilots, so be a good student- ask questions about everything, listen, and enjoy the process. If you haven't already, join the club. Gratuities (like donuts and coffee) aren't necessary but are appreciated. If you're learning on his equipment, a gallon of fuel makes a nice incentive too if you'll look and see what he's using.