Giving feedback to student....START WITH SOMETHING POSITIVE! "Great job on your posture". "Excellent hand position". "I really like your attention to playing notes accurately". Note the words great job, Excellent, I really like.

THEN ask them to tell you what they think they can do to improve and make your own suggestions. Finish with "remind me what you are going to do to continue improving". High five, fist bump. "I'm proud of you".