Pursue meaningful church membership. That is, move toward having a membership that is composed of genuine Christians who regularly attend the church and are committed to its teaching. Christians will preserve true doctrine. Non-Christians won’t. (Click here for more on meaningful membership.)
Recognize a plurality of elders (Acts 14:23, 20:17). Having multiple godly, doctrinally sound men leading the church will help ensure doctrinal soundness and unity over time.
Develop a culture of biblical and theological literacy. In order to do this a pastor should preach expositionally, teach theology, give away books, and personally model the practical importance of sound doctrine. The members of the church should diligently study the Bible and spur one another on to grow in their love and obedience to God.
Expose false teachers. This is especially your job if you’re the pastor. This doesn’t mean you need to inform them about every bad book or misleading movement they’ve never heard of. But it does mean teaching them to measure every new teaching according to Scripture so that they know how to recognize a false teacher when they see one.