When teaching someone the kayak roll, you must first know how to roll a kayak yourself so that you can properly diagnose and instruct the person you aim to teach. Choose a calm protected place where you will be practicing that is shallow enough to stand. You will be getting in the water so be sure to wear your pfd.
The person who is being taught to roll should know how to successfully wet-exit the kayak prior to trying to learn to roll. Additionally, it is helpful if the person learning to roll has perfected the hip-snap.