What a Good Pitch Shows

A good one-sentence pitch is useful in many ways other than just pitch parties on Twitter. Creating one before you even finish your book can reveal weak points. And, if you can't effectively communicate what your book is about quickly and easily, it will be hard to get people interested in it. It should reveal three things about your manuscript:

• The Problem (the main conflict): This is often the catalyst, what propels the entire book into action. It's big, and it should be toward the beginning of the book. Big means something different for each book, protagonist, and often genre. Someone dies, is kidnapped, fired from their job, a relationship ends, etc.. 
• The Stakes (Obstacles): What is at stake for your character? What stands in your character's way? You shouldn't list it all out in a one-sentence pitch, just go for the main thing.  
• The Solution (the journey): What has to happen for your character to overcome the obstacles in their way and obtain their goal? What type of journey must they make, or things must they do.

It can look like this (but doesn't have to follow it exactly): When The Problem happens to Your Character, they risk The Stakes, if they don't The Solution. 

If you write this before finishing your book, you'll be surprised at how much it will help you hone in on the things that matter most, and keep you moving toward that end goal. Happy writing and pitching!