Over the holidays an acquaintance wrote to ask how I bagged my publishing deal. A cousin had a book he was hoping to sell; did I have any advice? As it happens, I do.
There are two ways to get your book published. You can find an agent who does all the dirty work or cut out the middle person and negotiate directly with the publishing house. Barring a personal contact or some other "in" big houses only work with agents. And some small houses won't work with agents.
Regardless of the route you take, you must have a query letter and a writing sample (typically 5-10 pages of the book you're trying to sell). The writing sample need not be the opening scene but it should be the strongest bit of writing in the whole book. I chose a flashback I was proud of and didn't introduce it with any explanation of plot or character. This is only my personal opinion but I think long prefaces are tedious and unnecessary. Editors and agents are looking for the quality of the writing and the sample should speak for itself.
The query letter requires a little time and copious tears. First, you'll need a synopsis (there are guides to writing synopses and sample synopses all over the internet). And when I say "first" what I really mean is a synopsis should be the very first thing you write, before a single word of the book. Because a synopsis brings plot holes to light. This is a much more efficient method for crafting a narrative than the one I used which was to write two drafts of the book, pen the synopsis, then slap myself on the forehead.
Launch into the synopsis right after the salutation. My synopsis ran three paragraphs ending with a summation of themes. You could name two comparative titles or authors or if you're pitching to a specific publishing house reference books or authors from their catalogue that are like yours or concern similar themes. This is tricky because you don't want to give the impression you're covering already-trod ground. But you could frame it as: "picking up where Pride and Prejudice left off" or "in the epic style of Tolkein."
Next comes the bio. In a single paragraph list your awards, publications, and your MFA, if you have one. Unless it's related to writing or your book, don't mention your day job.
The final paragraph is the sign off. Make reference to the sample (i.e.: "the first five pages are attached" or "a scene from the middle of the novel is attached"), state the total word count, and say thank you. Make sure your contact info is somewhere on the cover letter. And I can't stress this enough: ONE PAGE ONLY. Here's the format:
Dear Publisher/ Agent:
Paragraph 1 - 3: Synopsis
Paragraph 4: Bio
Paragraph 5: Sign off
Unless you have a specific house you're keen on (that also accepts unsolicited queries) my advice is to start with agents. There are only a handful literary agencies, not every agent will be accepting new clients, and agents tend to specialize in specific genres. So research won't take long. Choose agents who look like they earn their keep. Who are their authors and where are they being published? Is the agent going to the big book fairs (London, Frankfurt)?
I'm a fan of simultaneous submissions. Submit to all your potential agents and then wait. If the query attracts interest, you'll be asked for the full MS. You should hear a yea or nay in fairly short order but if the agent doesn't specify feel free to ask for a timeline. A month is reasonable. If the agent passes on the book but they provide specific feedback (ie. the the pace is too slow or the ending fell flat), say thank you and politely ask if they might consider a revised version. Don't be shy about asking. You have nothing to lose and an agent to gain.
If you decide to go the non-agented route the process is more or less the same. The list will take longer to create because there are so many publishing houses and many of them specialize in some kind of niche. But again, I'd advise researching each house's catalogue, get a feel for what they publish, see how their authors have done, and try to find one that would be a good fit for your book. Everything else being equal, I would start at the top with the most established/ most well respected houses (perhaps the ones whose authors have won awards) and work through the list.
TL;DR: Do your homework and do it well. Aim high because you have nothing to lose. Practice patience and start writing the synopsis for the next book while you wait.