Teaching to Change Lives: Seven Proven Ways to Make Your Teaching Come Alive by Dr. Howard Hendricks.
Excellent, short (150 pages), practical, and highly encouraging. I love this book!
The Inductive Bible Study Handbook: Learn to read, observe, interpret, and apply the Bible by Sally Michael.
Teaching and small group leading is best done with a heart that has first studied, meditated on, and applied the truths being taught. This short and practical guide will help you do just that as you prepare your lessons.
(Image courtesy of nirots at FreeDigitalPhotos.net.)