If you are looking for small books whose content outweighs their size, I would highly recommend the Building Healthy Churches series, from 9Marks and published by Crossway. These are outstanding authors talking in a concise but substantive way about issues crucial to the health of the church.
Here are the books published thus far.
[Foreword by J. I. Packer]
“Compelling. Convicting. Encouraging. Probing. And most of all, entrancing. What a beautiful vision of what the church can be through the power of the gospel. How evident it is that the gospel has penetrated Ortlund’s own heart. Read it. Pray through it. Ask God to use its message mightily in your church and in many other churches as well.”
—Thomas R. Schreiner
“If ever you’ve been tempted to think that doctrine is boring, divisive, or just plain pointless, this is a book for you. Bobby Jamieson shows that sound doctrine is beautiful, life imparting, and deeply desirable. I hope this message goes far and wide.”
Jonathan Leeman, Church Membership: How the World Knows Who Represents Jesus
[Foreword by Michael Horton]
“Church leaders across many denominations will find this little book filled with practical ideas and good arguments that will help us cure Christians in our culture today of their allergy to church membership, pastoral authority, life accountability, and any limits to their personal freedom.”
Jonathan Leeman, Church Discipline: How the Church Protects the Name of Jesus
“Far too few biblically grounded, pastorally sensitive books on church discipline remain in print today. I know of none that is as exegetically accurate, practically relevant, and filled with real-life case studies of how churches should deal with a wide variety of common situations. On top of all this, Leeman is helpfully succinct and remarkably clear. Highly recommended!”
—Craig L. Blomberg
See my notes on the book here.
Mack Stiles, Evangelism: How the Whole Church Speaks of Jesus
[Foreword by David Platt]
“Mack Stiles is one of the most natural, effective, determined, indefatigable evangelists that I know. I would want to know what he thinks about evangelism, whether it comes in a conversation, a letter, or an entire book. In this short volume, Mack conducts a clear and biblical exploration of how church fellowship multiplies individual evangelism. Every reader will be inspired, encouraged, and equipped to be a congregational evangelist. For the sake of the church, the gospel, and the world, this book belongs at the top of your reading list.”
—R. Albert Mohler Jr.
Jeramie Rinne, Church Elders: How to Shepherd God’s People Like Jesus
“Most unsolved problems in church life can be traced back to defective leadership. Jeramie Rinne unpacks what the Bible has to say about the identity and activity of the local church elder with a freshness and clarity that is profoundly helpful. This is a book that elders can read together to their profit and one that will help a congregation to pray for and support its leaders so that their work will be a joy and not a burden.”
David R. Helm, Expositional Preaching: How We Speak God’s Word Today
“David Helm has written the most helpful, concise, and useful book on expository preaching I have ever read.”
“This little book is simply outstanding. It’s the best short book on preaching I’ve read. Helm’s advice is unfailingly wise, theologically informed, and extremely practical.”