If you are asking this question, it assumes that you're presently not experiencing the shotgun approach. Prevention is always easier than the cure.
Define missions for your church. If you don’t define it, then it becomes very difficult to figure out the boundaries of what is allowed and what is not.
Establish the missions priorities of your church. It’s important for leadership and decision makers to have a common understanding of what is significant and important versus all the rest. There are always choices between good, better, and best in ministry. One of the most difficult skills is learning how to say “yes” to the right stuff and “no” to all the good stuff that can keep you from doing the best stuff.
Also, there are missions ministries out there that are not even good or fitting for your church’s involvement. Commonly churches will identify pioneer evangelism, church planting, and leadership training among their top priorities. Further down the list may be such missionary activities as community development, field support ministries, and literature or media development.
This is not to say that these things could not be strategic and on target for your churches missionary interests. I.e.- your church’s priorities might be appropriately influenced by your constituency, particular skill set, or strategic focus. It might also be highly influenced by the target ministry population. For example, if you have a prayerful vision to reach unreached people groups in a creative access Muslim country, it may be of highest priority for you to support someone through a Business As Mission platform; strictly speaking, that person may not look like the traditional, full-time church planter, even though their daily activities support church planting as the long-term ministry result. Typical ministries which fall lowest on the list are relief and development efforts which are strictly humanitarian and don’t have a specific Gospel, evangelistic, or church planting development goal or component.
Set criteria for acceptance of missionaries for support. Included in the application process might be some review of their missions training and doctrinal alignment with your church. Many churches include specific requirements for accountability and communication, including prayer requests. We know of some churches who have unwittingly supported missionaries with divergent or even divisive views on important issues. Some churches have terminated missionaries who have failed to communicate frequently or well enough, thus preventing them from fulfilling their role in support and prayer. Clearly articulated expectations at the beginning will prevent problems and misunderstandings later. Train them early and, “when they are old” they will not depart from it.