Too many times writers feel they must have an agent before they can get a book published. The conventional wisdom is often that all writers do is write and agents do all the rest. It is true that agents help shape a writer's career, market the manuscript to the right publishers, understand the contracts, look for the best deals and best advances, help advise on marketing, and my goodness all else. Why would anyone ever think to "go it alone?"
Though it would be wonderful to sit back in your comfy little chairs and write whatever your hearts desire, that's not how the published world of writing works. If a writer wants to be published, the writer needs to know if the nonfiction book she's writing is something the public might want to buy. The writer needs to research on-line and in book stores to see what books are available in the area that she's wanting to write. If there are no books written on the subject of interest, that is not a good sign. Though there's a small possibility that it could mean there's an opening in the market, too often it means that the public isn't interested in buying anything on that subject or written in that style.
To get a book published through traditional publishing or agent, the writer has to write a book proposal. In this book proposal, the writer has to compare the book being written to what's already on the market and how it competes with those books on the market. A writer also has to study the various publishers and target the proposal towards that publisher's style. A writer needs to follow the standard length format for the book being written.
By the time a writer sits down to actually write the book, she knows so much about the publishing market, that it's sort of a waste of time not to use that information to direct the manuscript to the best suited market. For writers who market their own books, they have much more sense of how the whole publishing industry works, which in turn, makes them better writers. Plus, a beginning writer or one who's not a house-hold name needs to focus mostly on the smaller publishing houses. Writers Market lists hundreds of publishers who take un-agented manuscripts, so these are the ones you should target. If you are writing Christian material, use Sally Stuart's Christian Writers Market Guide. Publishers come and go so quickly that you need to use the most current version as well as look for updates on-line for the publisher you have in question.
If you have a niche book, you'll need to submit your manuscript to publishers yourself. A niche book is one which does not have mass market appeal. Academics, specific education techniques or subjects, diseases, specific hobbies, and other non main-stream writing needs the smaller publishers---and sometimes these are best suited for self publishing. Individual religions have their own publishing industry and are not huge publishing houses. These smaller publishers and university type presses are style represented in traditional brick and mortar book stores, so writers needn't think they are settling for less at all. Each book needs the specific type publisher best suited for its needs.
Also, smaller publishers are willing to take risks on unknown authors. Don't ever feel despondent that you haven't had a book published. Too often writers can lose sight of their goals because they think "why would anyone take a chance on me?" Publishers are always on the look out for new authors.
One of the best ways to find representation from a smaller publisher is to go to a conference where that publisher is making a presentation. Often, they will set aside appointments to meet with new authors and discuss your manuscript with you. They are hoping you will succeed just as much as you are hoping you'll succeed. Smaller publishing houses have more time to devote to individual authors.
You've done all the work, so go for it. Get out there and approach that publisher yourself either in by sending a book proposal or hand delivering your book proposal at a conference.

