Mentoring

I've never really had much formal mentoring and H and I have often leaned on each other for support with professional activities and research since we're in the same field and have similar research interests.  We even went up for tenure together!  I always joked that he should have been an honorary PhD committee member for me since I worked on my dissertation long distance for the last 2.5 years of my PhD.  It was easier to ask him which statistic might work better than trying to reach my advisor. 

We both managed to get through tenure this way with a little guidance from others at times and over the last few years I've started to feel that I can serve as a mentor to colleagues who are just starting the tenure track.  The only issue now is I don't have my own good experiences to draw on to be a good resource to this colleague.  How do I be a good mentor? Did any of you have mentors early in your career? Have you served as a mentor? We're supposed to start having discussions about this in my department, but I think many of us are in the same boat. Please share your thoughts!