Of course the first prerequisite for a missionary is that he or she be a person who has trusted in Jesus Christ's substitutionary death on the cross as sufficient payment to satisfy God's wrath against his or her own sin. How can you tell others about that which you have not experienced yourself?  See What is a Christian?

NTM requires that missionaries have a working knowledge of the Bible and a consistent walk with God. Those who do not have this knowledge may get practical training at one of the New Tribes Bible Institutes.  

No matter where you are you should be involved in your local church through attending meetings, participating in whatever ministries you are able; such as evangelism, teaching Sunday School, working with AWANA or other youth activities, small group activities or Bible studies, or whatever activities will help you teach, learn and grow as a Christian.

NTM highly recommends that missionaries have the support of their home church or that they have a solid base of encouragement from local churches. Throughout missionary training trainees are encouraged to participate in local church activities and build their relationship with their home churches. Practical ministry experience will be of great benefit on the foreign mission field, both in ministering to local people and to missionaries. 

After a screening process missionaries are accepted for training at a New Tribes Missions Institute (NTMI). At NTMI the students are taught, among other things, basic principles of Cross-Cultural Communications, how to teach the Bible chronologically, basic Bible doctrines, work ethics, and interpersonal relationships (how to get along with your teammates) with an emphasis on walking in the Spirit and gracious obedience to the truth. (Galatians 5:16)

When released from NTMI for further training, trainees go on to the New Tribes Language Institute (NTLI). NTLI is designed to give students practical training in language acquisition, learning language from monolingual people, Bible translation, phonemics, phonetics, practical training in technical aspects of setting up an office in remote settings, and other things technical things related to church planting.

At the end of the NTLI training missionaries prepare and move to the foreign mission field or the ministry that God has put on their hearts. Many people use up to a year to rebuild their relationships with their sending churches and further establish their prayer and financial support base.

Much of the first year after arrival on the foreign mission field will be spent in orientation to the customs and culture in the new country and in learning the language people there use in everyday trade. 

For specific information and applications, see: http://www.ntm.org/