I’ve used a number of resources to train church officers over the last 27 years. This one book has replaced virtually all of them. Now, along with G.I. Williamson’s Westminster Confession of Faith for Study Classes, I have everything I need to train both elders and deacons. The book runs you through the biblical warrant for officers, their qualifications and duties. It then discusses the role of both elder and deacon in detail, addressing areas of importance for each. Really, everything you need, save your confessional standards, can be found here.
Best Single-Volume Text for Training Officers