The easiest books to market are those with a very clear purpose or message that can easily be described. We would regularly ask authors to sum up the message of their book in no more than 50 words. It’s a good exercise to do because it forces you to focus on you core message and crystallise it. If you struggle to describe the central theme of your book in max. 50 words then it probably means you are trying to address too many issues.
There are what we call “soft focus” and “sharp focus” books. Soft focus books take a broad topic and then look at a number of themes around it. E.g. A book on Christian living that might include chapters on essential but diverse elements such as prayer, intimacy with God, forgiveness, spiritual warfare etc. Inevitably, each topic is covered quite superficially.
It’s easier – and far better from a publisher’s point of view – to write a sharp focus book. E.g. one that takes a single theme or aspect of something and examines it thoroughly.
If you’re working on a non-fiction book (We’re not necessarily suggesting you should try to sum up your novel in 50 words, though it’s not impossible if it has a strong theme!), try the 50-word summary and see how you get on.