If you want to become a successful and influential instructor, you will have to become a master of not only the martial arts but also of interpersonal skills with your students. The Art of Effective Feedback will become a cornerstone of your relationships with your students and of the ultimate success of your students within your program. Practice this advice and reap the benefits, ignore it at your peril!
Be sure to give feedback to students in the class on a regular basis. Try to make all feedback either positive or constructive, and avoid any negative feedback if possible. Negative feedback should only be used as a last resort when there are behavioral issues, rather than issues of poor technique; and even then, there are steps you should take before resorting to negative feedback.
Positive feedback is obvious. Comments such as "that was a great kick," "nice stance," "that's the best I've seen you do that kata (form)," "you really looked like you were trying hard in sparring today" go a long way towards creating a positive atmosphere and a comfortable environment in which to learn.
When you add the student's name to any of the above types of encouragement then your relationship to that particular student will improve almost immediately. The importance of using your students' names when giving feedback cannot be understated. If you get nothing else from this article, please remember that personalization of your feedback is often more valuable than the feedback itself!