Now in the church that was at Antioch there were certain prophets and teachers: Barnabas, Simeon who was called Niger, Lucius of Cyrene, Manaen who had been brought up with Herod the tetrarch, and Saul. As they ministered to the Lord and fasted, the Holy Spirit said, "Now separate to Me Barnabas and Saul for the work to which I have called them." Then, having fasted and prayed, and laid hands on them, they sent them away.
Acts 13:1-3

This is the first mention in the New Testament of officially sending out missionaries. Please note the following that should remain consistent regarding sending missionaries, even to this day:

Missions and missionaries are to be sent by local churches. Why? Because missionary endeavors ought not merely be about evangelism, but also about church planting. Who better to plant churches than those sent out from local churches?
Missionaries are to be sent from local churches. Missions is an extension of the church, not an individual adventure. Too often in our day, individuals want to serve in missions because they see it as an adventure. They may or may not even be serving in a local church. They connect with a “para-church” ministry and set out without any accountability to a local church. This is not the pattern set forth in Scripture. Nor should we support these “independent missionaries.”
Missionaries sent from local churches must be spiritually qualified. The church at Antioch did not send out just anyone. They sent out a couple of their premier teacher/leaders. Remembering that missions should primarily be about church planting, those sent should be spiritually qualified and experienced as officers of a local church. If they are not, how can they plant churches?

Missionary ministry is vitally important business. Let us insist that it be engaged in biblically.