The online book called Entering Mentoring, by J. Handelsman, C. Pfund, S. Miller Lauffer and C. Maidl Pribbenow, contains useful information for mentors. It is written for graduate students mentoring undergraduates in biology labs, but a lot of the information is relevant to other situations. In particular, you may want to read the following sections.
Below are links to some of the literature discussed in the 2006 mentoring seminar, together with summaries provided by the participants.
A summary of the surveyed literature, prepared by the student participants.
By D.R. Bacon, K.A. Stewart, and W.S. Silver, Journal of Management Education 23, 467-488 (1999).
Overview by Becky Vandiver.
by B.J. Millis and P.G. Cottell, Oryx Press, 1998.
Overview by Mark Robertson-Tessi.
by R.D. Woodberry and H.W. Aldrich, Teaching sociology 28, 241-248 (2000).
Overview by Jared Barber.