A how-to-write book. A rare one: intended for the people who write novels already. Like, indeed, his Writing the Breakout Novel, which perhaps you should read first.
However, this is his list of problems in manuscripts -- derived from his job as an agent. Followed by exercises on things from your characters, to voice, to tension, to how to be funny.
There are quite a few exercises, all of which presuppose you have a manuscript in hand. Might be interesting to try to apply in first drafts or pre-writing.