The elders need to continually be developing leaders. Bob Deffinbaugh challenges elders to be on the lookout for potential leaders and to take steps in developing them.
You can access the individual outlines for each lesson from the corresponding lesson pages below, or access the combined outlines here:
Lecture Outlines for Developing Leaders Series
Detailed Outlines for Developing Leaders Series
The Training of the Twelve by A.B. Bruce: This classic, written originally in 1894, is on the top ten reads for both Dr. Howard Hendricks (legendary teacher of Dallas Theological Seminary) and George Verwer, founder of Operation Mobilization. This book examines the ministry of Jesus to his twelve disciples. Short chapters, but deep in spiritual insight.
18 Words for New Elders: Excellent article for new (and longstanding) elders, summary advice from a variety of experienced elders.