If you're planning on writing nonfiction, then the first question you have to ask is whether or not you think yourself capable of embarking on this trying yet rewarding journey. With general non-fiction, there will always be space for a good new non-fiction book in the market. So, what makes a non-fiction book a best seller? Firstly, your book should be able to attract a considerable amount of readers; it has to be something that is new and interesting, preferably a topic that no one else has broached. Or, if you're writing on a topic that isn't new, then you should come up something that's new and interesting to contribute to the whole concept.