You have received probably an overwhelming amount of excellent advice, here. A few points I would reinforce are:

1) Communicate: before the flight, talk about what that flight is going to involve, a "flight plan". It may be as basic as flying the pattern with 90 degree turns (and when the student makes a 180 turn, say "that was a nice 180, but we are doing 90s, right?" Every new task should begin with the instructor demonstrating what it should look like, both as to the flight maneuver and the position over the field. If the student continues the same error, such as over banking, take the plane over and demonstrate what it is supposed to look like. Always let him know when you are taking the plane and when turning it back to him. Give feed back and encouragement at every opportunity during the flight. When he makes a good turn, acknowledge it, when he makes a bad one, gently point out what was bad about it. At the end of the flight, a short debriefing on how the flight went, what was good and what needs more work. Be encouraging.

2) Practice makes perfect, only if it's perfect practice. Do not let the student practice doing wrong things! Flight duration for new fliers should be very short, maybe 5 - 7 minutes. Most experienced fliers can enjoy flying as long as the fuel holds out. Not so with a newbie. Remember back in your own first few flight experiences. You were typically "behind the plane", spending your energy trying to correct things the plane is doing. That can be quickly exhausting to the pilot's concentration, and when the concentration is exhausted, then bad things start to happen, and the pilot is concentrating on crash avoidance, not flying. Bad flying habits come from this. Be attentive to when you see the student starting to make mistakes he was not making at the beginning of the flight. That is the clue that the "overload" point has been reached. When you see the student is getting more comfortable and not struggling with the concentration, extend the flight times, accordingly.

3)Require attentive performance, and be consistent. Nothing succeeds like success. I like to get the new pilot taxiing his plane right away. If field conditions permit, have him taxi back and forth on the runway to get the idea of the differences in slow taxi and faster taxi on the field. With many students, they can be good to do their first take off on their 2d or 3rd flight. Everybody is not necessarily compatible with everyone else. If you encounter someone who, for one reason or another, is not a good fit with your style, face up to it, and encourage (or require) a change. When I instruct, it's "my way or the highway". My way is flexible, to a point, but if I am flying someone who just wants to goof off all the time, I just land the plane, shut down the engine and end my instruction. Maybe another instructor will be more effective with that person.

I want to encourage you to be an instructor. You will have opportunities to help others, and you will find personal satisfaction in doing that. Best of luck to you.