The mentoring that I received as an undergraduate paved the way for my entrance to grad school and my future research. The Council on Undergraduate Research has a publication devoted to the topic of mentoring undergraduate researchers, summarized at the Undergraduate Research Laboratory. Among the suggestions:
- Actively recruit students
- Work on numerous projects together
- Recognizing your limitations as a mentor
None of these are groundbreaking, but they may be particularly helpful for assistant professors who are just starting out and do not have a large number of students that they would be interested in working with.
Memoirs of a SLACer 
[…] institution regularly went out of her way to ensure that I knew what was going on. Unlike mentoring undergraduates or graduate students, at the faculty level I think that successful mentoring is mostly about […]