There's a thread at MetaFilter entitled "What single book is the best introduction to your field (or specialization within your field) for laypeople?" It concerns the hard sciences and mathematics in the main, but the same question is fair for the ministry, church administration or even theology.
Not that any one book would be perfect or comprehensive, but these questions help people find resources when they would otherwise risk failure, sunk under a wave of competing resources. Additionally, there is a traditional of Universalist practical manuals I wouldn't mind seeing revived. These were 16mo pocket-sized books that had a little theology, spiritual guidance, history, statistical information and oftentimes polity justifications and model constitutions for forming churches and state conventions.
So, what single book would you give a layperson considering (lay?) ministry, church administration and theology respectively?