- The Scriptures (especially The Book of Mormon)
- The Preach My Gospel manual
- The Gospel Principles manual
I have read a lot of other mission prep books, listed below. All of these are good books, though some are better than others.
- Raising Ourselves to the Bar by Brad Wilcox
- What I Wish I’d Known Before My Mission by John Bytheway
- Raising the Bar: Missionaries to Match the Message by Ed J. Pinegar (also available in Audio CD: Raising the Bar)
- How to Be an Extraordinary Missionary by John Bytheway
- Prepare With Honor: A Guide for Future Missionaries by Randy L. Bott
- The Ultimate Missionary Companion by Ed J. Pinegar
Then, of course, there is the book I wrote in 2011–Mormon Mission Prep: A Practical Guide to Spiritual and Physical Preparation by James R. Smith. The book is a little dated now, but it is still full of great information, and it’s a great deal–$10 for a brand new copy.