Mentors are Human Beings
Make the effort to relate to mentors on a personal level and share a dumb joke sometimes. Value their time and expertise and refrain from informal phrases like asking to “pick their brain.” And if you run across an article (etc.) that you find really helpful, pass it up the food chain; your mentor might enjoy it too.
Eye on the Prize
Ask specific questions to your mentor, seeking to gain specific insights. It is up to you to take the knowledge you gather and apply it in a way that is instructive to your career. Read more here: http://entrepreneurs.about.com/od/businessmentoring/a/businessmentor.htm