The first step in a mentoring relationship is to figure out what the expectations are on each side. What does the person being mentored expect from the mentor? How is the relationship going to work in concrete terms? How often will you meet? Does the person (I refuse to write "mentee") want you to read her work and offer commentary, or offer more general advice about navigating the profession? What are the goals, aside from the obvious, inevitable answer (getting tenure)?
The mentor needs to let the person know what to expect. For example, if I am a mentor to someone in a quite different specialty, I cannot offer specialized advice. Maybe I can read your stuff, but won't have time to read every article for style. Maybe I'll be there when you need me, but we don't talk formally every month. Some people consult their mentors about important decisions only, some want a daily rapport.