Nonfiction books often stay on the market and produce royalties for many years. Educational, reference, travel, hobby, fitness and religion nonfiction do quite well. The finished book should be well organized and clear to the targeted readers.
Each publisher has its own guidelines that must be followed for success. The author should list credentials, provide references and cite sources in a cover letter. Provide a detailed outline and sample chapters to give the editors an idea of your writing style.
Today's fiction must be fast paced, relevant to current tastes and have clear conflict. The book should begin with action or dialogue, which will instantly immerse the reader in the story. Character motivation needs to be clear close to the beginning of the book, and it should tie in to the main conflict. The setting should be clear and well drawn with more showing than telling. Employ the senses throughout the book for the most favorable reviews from editors and readers. Follow the conventions of the genre. For example, in romance, the hero and heroine must get together by the end of the story. In mysteries, the murderer must be caught. In Westerns, the good guy always wins.
For fiction novels, most publishers look for a well-written query letter and short synopsis before requesting sample consecutive chapters. The query letter should start with a one-paragraph story blurb, a short version of the author's bio, and details about the genre, word count and when the full story can be delivered. The short synopsis should be one to two pages and include the character motivation, the conflict, the main plot, major turning points and the theme of the story. Always include how the story ends in the synopsis. If the editor requests a full proposal, reiterate the information in the initial query letter. Submit the first three chapters and a more detailed synopsis of the book. The general rule of thumb on the longer synopsis is one page per 10,000 words of the completed story.
The conventional publishers have everything set up for the success of each book. In addition to only acquiring what they feel will sell based on their history and experience in the market, they offer editing, distribution to places authors don't have access to and an accounting department. They often provide resources and promotional materials to the author.
Print-on-demand publishers have grown in number over the past several years. Some have editorial guidelines, while others will print whatever someone is willing to pay for. Since each book is printed as it is ordered, they are generally more expensive than those published conventionally with a 20,000 print run. The advantage to a POD is that the author can have the book printed more quickly and only order what is needed. Types of books to consider for print on demand are family histories, memoirs, and books that are turned down by conventional publishers (if the author has a ready market for them).
Self publishing also has its place. Novels rarely do well if they're self published, but self-published nonfiction can be a viable option for those who are on the speaking circuit. Often the cost of a workshop can include the price of the book, or the book can be sold after a lecture. With a captive audience, the author is likely to see a profit from self-published books.