As a current student, I absolutely love supervision when it's an opportunity to learn and not be scolded about what I did wrong or berated when I didn't do something exactly the way my supervisor wanted or would have. If I had to pick one most important quality for a supervisor, it would be them fulfilling a mentor-mentee relationship where I'm allowed autonomy and not intimidated to ask questions. If I mess up, let's talk about what I did and my thought process as to why I did it. Then make it a learning experience about your approach and how I can think from a different perspective. If I did something well? Positive reinforcement is a great thing for anyone to hear, especially a supervisee.
It seems self-explanatory, but MAN there are some people out there that struggle with being a positive, encouraging mentor.