Books
See also this list of Articles on the preparation and development of mathematics teaching assistants.
Case, B. A. (Ed.). (1994). You’re the professor, what next?: Ideas and resources for preparing college teachers. (Vol. 35). Washington, DC: Mathematical Association of America. 
!DeLong, M. & Winter, D. (2002). Learning to teach and teaching to learn. Washington, DC: Mathematical Association of America. (review) 
Friedberg, S., Ash, A., Brown, E., Hughes Hallett, D., Kasman, R., Kenney, M., Mantini, L., McCallum, W., Teitelbaum, J., & Zia, L. (2001). Teaching Mathematics in Colleges and Universities: Case Studies for Today’s Classroom (Faculty Edition). Providence, RI: American Mathematical Society.BCCase: The Boston College Mathematics Case Studies Project website
Abstract: Progress in mathematics frequently occurs first by studying particular examples and then by generalizing the patterns that have been observed into far-reaching theorems. Similarly, in teaching mathematics one often employs examples to motivate a general principle or to illustrate its use. This volume uses the same idea in the context of learning how to teach: By analyzing particular teaching situations, one can develop broadly applicable teaching skills useful for the professional mathematician. These teaching situations are the Case Studies of the title. Just as a good mathematician seeks both to understand the details of a particular problem and to put it in a broader context, the examples presented here are chosen to offer a serious set of detailed teaching issues and to afford analysis from a broad perspective. Each case raises a variety of pedagogical and communication issues that may be explored either individually or in a group facilitated by a faculty member. Teaching notes for such a facilitator are included for each Case in the Faculty Edition. The methodology of Case Studies is widely used in areas such as business and law. The consideration of the mathematics cases presented here will help readers to develop teaching skills for their own classrooms.
Intended Use: Faculty edition--Faculty in mathematics. Especially useful for faculty concerned with TA-development. Also useful for graduate students and younger faculty who wish to work through the case studies independently, and for faculty concerned with the education of high-school math teachers. Graduate edition--graduate students in mathematics, especially graduate students participating in a program which uses the case studies. (review)
How To Teach Mathematics, Second Edition, by Steven G. Krantz. American Mathematical Society, 1999. Softcover, 307pp, $24.00. ISBN 0-8218-1398-6.
Rishel, T. (2000). Teaching first: A guide for new mathematicians. Washington, DC: Mathematical Association of America.