How can foreign missionaries best serve countries that already have an established Christian church?

1. Learn the local culture. The apostle Paul adapted his lifestyle to non-Jews (and Jews!) he evangelized (see 1 Cor. 9:21). This means that he paid enough attention to notice how their culture differed from his. So, rather than hopping off the airplane and beginning to correct everything, a missionary should ask questions about the worldview, presuppositions, and customs of the people to whom they are trying to minister.
2. Partner with the local church. If the pioneer stage of missions in a country is over, would-be missionaries should not do all their planning in isolation from the indigenous church. Rather, they should plan together with local church leaders. If they do, they will likely see that their primary focus should not be on bringing over even more foreign missionaries, but on equipping local Christians to be missionaries to their own people and region.
3. Join a local church. If foreign missionaries do not join a local church, they project to local Christians the spiritually disastrous message that it doesn’t matter whether or not a Christian is a member of a local church. Therefore, foreign missionaries should find some way to retain a partnership with their sending church while also joining, engaging in,and being accountable to a local church. 
4. Pursue equity in Christ’s body. If missionaries come from a country that is rich compared to the country they are serving in, they should consider how they can leverage their resources to bless local Christians, particularly with sound biblical resources.
5. Pursue a pure church at home. A country can only export what it produces. If the church in your home country is churning out heresy, your efforts to build the church abroad may be torn down by your fellow countrymen. So missionaries should do what they can to promote pure doctrine and healthy churches in their home countries.

(Most of this material has been adapted from Conrad Mbewe’s article, “How American Christians can help Christians in Zambia”)