Prepare yourselves mentally. A mission requires a great deal of mental preparation. You must memorize missionary discussions, memorize scriptures, and oftentimes learn a new language. The discipline to do this is learned in your early years. Establish now the daily practice of reading the scriptures ten to fifteen minutes each day. If you do so, by the time you reach the mission field, you will have read all four of the standard works. I urge you to read particularly the Book of Mormon so that you can testify of its truthfulness as the Lord has directed.
Ezra Taft BensonTo be a successful missionary one must have the Spirit of the Lord. We are also taught that the Spirit will not dwell in unclean tabernacles. Therefore, one of the first things a missionary must do to gain spirituality is to make sure his own personal life is in order.
Ezra Taft Benson