Several observations ..
(a) One should ensure that the student is well-briefed and has access to a suitable, pertinent and defined set of reading material. You cannot expect the student to understand if he/she doesn't have a reasonably clear idea of where the goalposts are.
The instructor's expectations of student progress should be reasonable considering the individual student's abilities to learn. (The military can afford to scrub people early on against a milestone assessment system but this is not overly appropriate for recreational flyers). It is not appropriate for the instructor to expect student progress against criteria which are not achievable, for whatever reason, by the particular student. On the other hand, one should push the student within the particular student's capabilities.
(b) demonstrate skills exercises to the extent reasonably necessary but no more than that ... most skills exercises are best learnt by a little demonstration and lots of supervised practice.
An appropriate level of constructive comment assists student understanding and retention. Conversely, destructively negative comment (sarcasm, etc) should have no place in the learning process - this is not to suggest that negative comments are never appropriate, but warranted praise and consistent encouragement tend to get better results.
(c) accept that a student will provide frustration for the instructor and do your best to overcome your own frustrations at apparently slow progress by the student. The instructor's attitude can colour the student's thinking very rapidly and self confidence exits quickly with predictable results .....
(d) while some instructors may be more suited to the job than others for whatever reasons, we all can do a better job today than we did yesterday if we maintain a "good" attitude ourselves.
(e) keep clearly in mind the fact that the student is paying big dollars for the privilege of learning to fly. You owe it to the student to give him/her the best value for the dollar according to your own ability.
Just my twopence worth ...