Sam, the toddler has it right. A few insights I’ll add...
I’m a lawyer in real life and have my first book coming out with a mid-sized Christian publishing house in 2008 (it’s a nonfiction book offering practical Biblical counsel on everyday legal matters). Like virtually all first-time authors, I did it backwards - I wrote the book, then sought a publisher (really you’re supposed to sell a publisher on your idea, then write the book).
Be careful out there! Scams abound - fake agents, fake agencies, fake editors, fake book doctors, and fake publishing companies - plus some various “joint” or “partnership” alternative publishers that are merely disguised vanity houses.
Best advice I got at the beginning of the process: Money always flows TO the author. If you just go by that rule, you’ll safely navigate the minefield.
Start educating yourself by reading EVERYTHING on the Writer’s Beware blog ( http://accrispin.blogspot.com/ ) and every link they post. Seriously, invest a month or so in reading all that and you’ll be in solid shape, ready to face the realities of the publishing industry.
Now that I’ve signed my contract (two weeks ago) and await my modest (very) advance, I’m gearing up for the 75% percent phase: Promotion. I actually love this part - I care deeply about my message and so I have a passion to sell the book that goes beyond dollars (if I were to calculate the hours I poured into this project over the 5 years I worked on it using my regular hourly billing rate, I believe I would have to sell an infinite number of copies to break even!)- so, I guess I’m saying, make sure you love what it is you’re writing about!
I usually write a 40-page (or so) book proposal that describes the premise, who the market is, how to work the market and get publicity, chapter titles and summaries (that can change as I actually write the book), my bio, tear sheets and clips of other things I’ve done, DVDs of TV appearances (The View, Fox, ESPN) and tapes of radio interviews (local, national and a few overseas), and a tentative preface or foreword, plus maybe a chapter or two. http://lisaekus.com/literary-proposal.asp
I sell the book idea through the proposal, really a marketing tool. With this, you sell the manuscript and yourself-—and they go hand-in-hand. First you have to "sell" an agent. Then, if an acquisition editor likes it, he/she then has to sit down with a board of his/her peers and sell the idea to them. If it gets a thumbs down, you don’t go and spend 2 weeks on a bender, you simply tell your agent to keep pushing at the next publishing house on his/her list. http://lisaekus.com/
After I get a contract, THEN I write the book. Why spend months/years writing a manuscript that we can’t sell?
The proposal will get you a contract and an advance, and once all the details are worked out, that’s when I write the book.
Acquisition editors will read a proposal, especially if you have a good agent who will send your proposal to publishers who she knows have an interest in my subject matter. I don't waste much time with websites of writing "experts." Many of them are put together by someone who has sold 100 books of poems with LuLu or just had an article published in the hometown paper with a circulation of 1,500. There are a LOT of them out there. I also quit going to writers groups. They all to often consists of unsure writers who want to know all about how to handle a book tour, getting on Oprah, what they will insist upon in their contract, and how much money they will make. The cart, all too often, is placed well before the horse with these people. I know. I've been there. Talk to published authors and read some how-to books from those who have really been published---and least one time by a traditional publisher. Pay a few bucks for a phone consultation with authors who have an agent, who have been published with consistentcy through various means (traditional, self-published, subsidized, etc.) and who know the advantages and disadvantages of each approach); and then close your eyes and jump in! I go crazy when I read postings on writing web sites (and FR) of people with 10 manuscripts in their closets but haven't done a thing to get them ready for the publishing process. What's it going to take? Eleven manuscripts? Twenty? Fifty? Cut the BS, and just do it---but have a plan. Having someone say "No, it's not what we're currently looking for" is not the end of the world. Rejection is just one part of the process. Deal with it. I know it's so much safer to talk about your unread manuscript than have someone tell you it's not what they're looking for. No guts. No glory. Just DO it!