Don't take additional time or call at a late hour without your mentor's permission. He or she will likely give you advice or offer suggestions. Take that advice to heart, and try out the suggestions. Stretch yourself a little and try new things. Most importantly, let your mentor know that you took the advice and what the outcome was.
Mentors like to see the results of their efforts.
Follow through - Follow through with what you say you're going to do. This means returning phone calls, showing up for meetings, following through with assignments, and so forth. Nothing is more discouraging to a mentor than a mentee who doesn't follow through. If you can't follow through with a commitment, let your mentor know as soon as possible. Explain why you can't do it, and negotiate an acceptable solution.