One of the most frequent questions I get asked is how I got my first book of photography published. There is no easy answer. Getting published is a complex process, to say the least. However, there are a few things that I would recommend you do, and a few things I would recommend you not do, in order to increase your chances of success.
Firstly, make sure you have a project worth publishing. This may sound simple enough, but you would be surprised how many "press-ready projects" I've seen that are anything but ready for publication. Publishing a book of photography is not like merely making a photo album and then sending it out into the world. The narrative needs to be tighter - there needs to be a story. You also need to make sure the body of work is well edited. If you project contains two hundred images, you should aim to publish around fifty or sixty, not the entire two hundred. This is also a common mistake.
Next, I would strongly recommend producing a mockup to present to publishers. It's one thing to see a string of photographs and read an artist's statement, quite another to actually see your vision of the proposed book. There are many easy ways to do this now given companies like Blurb and Lulu, just make the book and produce a few copies to show around. Another option would be making a book directly from iPhoto. Which ever option you use, try to make the book as close to what you actually envision as possible.
Consider your proposal from an outsiders point of view. Are you known as a photographer? If not, what makes you feel your book will be of any interest to anyone? Publishers are in business to sell books, not to stroke egos. If you've never been published in magazines or exhibited in galleries chances are your project will be a hard sell to a traditional publisher. Rather than chasing an impossible dream, you may want to consider other options for promoting your work.
An artist's book is an obvious alternative. That is, produce the book yourself. Self-publishing is not to be discounted. It's true that there was a certain stigma associated with self-publishing but this is all but gone today. If a book is good, it's good. Although the self-publishing route is still arguably harder in the literary world, it's long been a common staple for photographers. Famous photographers like Martin Parr have been making and self-publishing artist books for decades. You could simply make your book with a company like Blurb and then market it, but if you truly want to be set apart from this more typical self-publishing, then make a limited edition book. A better choice of printer would be someone like Milk Books where you can produce a really high quality book (such as their Moleskin line) in limited run. Make twenty-five copies and hand number and sign them. Now you are not only selling a book, but an actual piece of collectable art. This option has turned out to be much more successful and profitable than a traditional book for many photographers.
Whatever you do, don't simply send your photography out to every publisher you can find on the internet. This is a wast of time and money. You will also likely annoy a certain number of editors in the process and they may not forget your name easily. Send your work to small presses if you are not William Klein or Roger Ballen. These operations are usually a one-person show and you can get to a real human being that might be willing to listen to your proposal and look at your mockup. How do you find these presses? The best bet would be to look and see who has published your colleagues and friends or other photographers whom you follow. Who has published similar work to your own, for example.
If you do land a deal to produce your book, beware of the process. Publishing a book looks like a lot of fun - from the outside. It's really a very long process and can often be filled with truly frustrating moments. Editors for the press may chop parts of your project, change your title or even rearrange the sequence of photographs. Usually the press, good ones at least, will involve you in these changes, but you may not be able to fully prevent them. You will need to be prepared for some give and take in this relationship. Also, when your book is finally published the truly hard work begins - selling it. Authors have a significant role to play in promoting and selling their books these days. You need to be prepared to do some major leg work, especially for small presses on tighter budgets. If you don't think you can sell your book, then don't get yourself trapped in a book contract with obligations (either implicit or explicit) to sell and promote. No publisher today will allow you to sit and home and wait for them to do all the work. Furthermore, no book just sells itself. It doesn't happen.
So, yes, getting published is an uphill battle. A small press that I know received over eight thousand submissions during a one month period this year. That's crazy. Given a situation like this you might almost say getting published is akin to winning the lottery. In fact, your chances might be better with a scratch ticket. Despite this depressing fact, if you have a project that is unique, truly good, and well put together, you should pursue getting it published. Just keep your options open and don't expect a letter from Benedikt Taschen anytime soon. Consider artist books, self-publishing, and co-projects with small local presses. If you have a project that is meant to be a book, chances are it will be one - just give it time and keep pounding the pavement. Just remember, the idea that one mails out a submission to a publishing house, get's accepted, and then sits back and collects royalties is a myth - unless, of course, you're Stephen King.
Finally, buy photography books by emerging artists. If you, as a photographer, are not buying other people's books it's kind of presumptuous to assume that your book should be brought into print. Who's going to buy it? The world of photography books by emerging and amateur artists is a community. You need to support your fellow colleagues and they will support you. If everyone is buying photography books, getting them published will become a whole lot easier.