Sticky Church by Larry Osborne. While I do not agree with all of his conclusions (such as the leader of small groups leading in Lord’s Supper apart from the assembly), he does give some helpful tips on the importance of these relationship-building groups. And without any marketing!
Why Small Groups? Together Toward Maturity, edited by C.J. Mahaney. My favorite of this group. This gives a wonderful rationale behind why to do these groups in the first place—not simply addressing the how. Critical book for your small group ministry.
Activate: An Entirely New Approach to Small Groups by Nelson Searcy and Kerrick Thomas. Practical, but sparse on Scripture.
Creating Community: 5 Keys to Building a Small Group Culture by Andy Stanley and Bill Willits. I’m a huge Andy Stanley fan and have read most of his books. This book does not disappoint!
And needless to say, the book of Acts!
What books have helped you?