As far as I can tell elders, pastors, bishops, overseers are synonymous terms throughout the New Testament (Acts 20:28; Ephesians 4:11; 1 Peter 5:2). They are clearly seen as the human leaders of the church. I would tend to agree with Ed Stetzer that ?the church should be led by a group of pastor-elders who serve in covenant relationships with one another?, as elders are always spoken of in a plurality, possibly as a way of protecting both the church and its leaders.
While the specific duties of an elder seem less clear, much of the criteria for the role appear to be character based. The biblical requirements can be seen in 1 Timothy 3:1-7 and Titus 1:5-9. Elders ought to have the capacity to boldly declare as Paul did, ?Follow my example, as I follow the example of Christ? (1 Corinthians 11:1). There does not appear to be any duty that is beneath fit for an Elder, however the capacity to preach and teach seems to be a primary differentiator from the requirements the deacon.
In practice elders lead the overall direction of the church (1 Timothy 5:17). They can do so through preaching and teaching (1 Timothy 3:2), being an example (Hebrews 13:7), praying for the sick (James 5:13-14), encouraging people and refuting false teachings (Titus 1:9), prayer and ministry of the word (Acts 6:4), amongst many other tasks.