As We Meet Together Again - President Thomas S. Monson

...every worthy, able young man should prepare to serve a mission. Missionary service is a priesthood duty—an obligation the Lord expects of us who have been given so very much. Young men, I admonish you to prepare for service as a missionary. Keep yourselves clean and pure and worthy to represent the Lord. Maintain your health and strength. Study the scriptures. Where such is available, participate in seminary or institute. Familiarize yourself with the missionary handbook Preach My Gospel.