The one clear pattern of a sending mission that we see within scripture is provided by Acts 13:1-4. Most mission organizations will allude to some of those verses whilst constructing their procedures. However I believe that when studied closely these verses actually contradict the majority of missionary practices that we have today.
The key verse to my interpretation of this passage is the first one:
Act 13:1 - 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.
There are three items that I would note.
Whilst the first verse is the key to my interpretation it is the second verse that is probably the more controversial.
Act 13:2 - 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."
Today it is expected that a missionary will receive the calling to go and serve and that they will then bring it to their church leadership who will ratify the decision or otherwise. However that is most certainly not how it was done in the first four verses of Acts 13. Here the church leadership were praying and fasting communally and they were all convicted of the need to separate out two of their own number. This gives at least three added levels of security over the approach we take today. Firstly if the call wasn't real it wouldn't have come to all of them and secondly the high price that the church was going to have to pay ensured that they would pray long and hard about what they were going to do. Thirdly this was a team that knew each other and prayed for each other regularly; they each had all of the information they needed to make their decision.
I should perhaps pause and mention the Holy Spirit. I am sure that the correct answer when asked why the Antioch mission was so successful is to say that they were praying and fasting in the Spirit and that the two missionaries were sent out by the Spirit. I am certain this actually is the cause of success. However as each believer has the indwelling Spirit we either have to accept that there is no requirement for teachers, preachers, elders or exhorters within the Body of Christ or we have to accept that God works through a blend of Spirit and Spirit inspired people to achieve His ends within the church. Given we accept it is the latter then it behooves us to ensure that the right people are in a position to make the decisions they make correctly. Thus I claim the Spirit was able to work because the right people were being asked the right questions and were thus able to deliver Spirit led answers.
For me the central thrust of this passage is therefore that successful Mission can occur when a church is Spirit led to split its' leadership in half and commission one half to engage upon mission activity. It is not difficult to envisage the cost that Antioch bore (losing 2 of a 5 man leadership team) or to imagine the degree of commitment and ownership that the congregation felt as the 'mission reports' trickled in. In fact Acts 14:26-28 tells us that subsequent to the missionary journey the missionaries came back to Antioch to report and to resume their roles.
Those that object to my interpretation here will argue that it is too damaging to the home church if they sacrifice such a key part of their staff. Far better to sacrifice a few students from college and an obscure Sunday School teacher or two rather than to threaten the very fabric of the church. I disagree. The leadership did not completely fragment; it split in two. Actually 60% of the leadership remained in Antioch. That would leave behind enough leaders to ensure continuity. But it would also leave a void and then that void would become the impetus for new and fresh leadership to emerge. It is interesting that when Paul and Barnabus returned again in Act 15:35 we find them fighting for platform space with all of the new preachers and teachers the Lord had grown into the void they had left!
In summary I believe Acts 13:1-4 should be the template for modern missionary work. The pattern is simple: the Spirit calls a church to split the leadership in half. The proven, trusted and already gelled team of teachers and preachers then goes out to proclaim the word of God. They retain their role in the home church and continue to come home as appropriate. The Lord then fills the space they leave behind with new leaders from the sending church.