1. Clarity on the gospel of grace. There are many counterfeits, not least the distortions of the gospel that make sin something you need to work off or blow off. Listen carefully for the comfort and the call of the gospel. First and foremost, listen for Jesus saying, "I do not condemn you." But keep listening for "Go and sin no more." The order is very important. The removal of condemnation comes before the call to obedience. But both need to be there for the church to preach the gospel.
2. Christ-centered preaching. You might have expected me to have said "expository preaching," but it is very possible to give an exposition of a text of Scripture without ever getting to Jesus Christ. This is especially true of preaching from the Old Testament. I don't remember who said this, but if the exposition of the Old Testament you're hearing wouldn't be thrown out of a synagogue, then the preacher isn't preaching Christ. Exposition of Scripture is the means by which we get to Jesus. But it is the means, not the end of preaching Jesus Christ and him crucified.
3. Theologically informed public worship. Are the basic elements of worship present: public reading of Scripture, exhortation and teaching from Scripture, songs, prayers, the sacraments of baptism and the Lord's Supper? In addition to these basic elements, look for songs with lyrics that exalt Jesus Christ and deepen your appreciation for and understanding of the gospel of grace. I'm not saying that short songs like "I Love You, Lord," have no place in public worship, but what I am saying is that if the content of the songs for public worship as a whole are shallow, it should give you pause.
4. Hospitable people. If the gospel is really doing its work in a community of Christians, they will love strangers, and not in that smarmy, fake, "I'm-glad-you're-here-because-I'm-supposed-to-be-glad-you're-here" kind of way. I mean that you feel genuinely welcomed and loved by the people as you meet them and spend time worshipping with them.5. Church discipline. Church discipline has gotten a bad wrap. The discipline of the church cannot be reduced to the final, punitive kind, but must include the formative type as well. Church discipline happens when the members of the church are willing to turn one another back to Jesus in loving calls to repentance, through encouragement in suffering, and exhortations to grow in grace.
6. Mercy for the poor. First John 3:17 says that if we who have the world's goods and behold our brother in need and close our hearts against him, we don't have the love of God in us. Thus it is a test of bona fide Christianity that the church cares for its poor. More than that, our care for the poor, though it should prioritize the believing community, should move beyond the church to the broader community: "Let us do good to all people, especially those who are of the household of the faith" (Gal 6:10).
7. Concern for the lost, evidenced by a church committed to personal evangelism. And by "committed to personal evangelism" I don't mean a church that has evangelistic programs, but that the people love their neighbors enough to tell them about Jesus. So look for a sincere interest in reaching the lost with the gospel of grace on the part of the pastors and the people in the pew, not as a notch in their belts, but because they are truly lovers of people as people, not as evangelistic prospects.