So, caveat: this isn't meant to be a complete list. I'm sure I'll revisit this post and add to it as time goes on, but I've been thinking about it for awhile now and would rather share it with you sooner than later.
So, without further ado: what can you do to sell you book, and more importantly, when should you do what?
1. Completion of your novel. Congratulations! You've written an entire novel (~60,000 – 100,000 words)! Now go edit it. No, don't tweet about how awesome your book is (yet). Edit.
2. Six months later... congratulations again! Between your critique group, your trusted first-readers, and your biggest editor/critic (i.e. you, at least at this point), you've polished your novel to a high lustre. Such a high lustre, fact, that you've begun using British spelling and grammar without even realising it. Ace! (Apparently you are also stuck in the 1980s.)
Have you written a truly smashing query letter yet? You have? Ace again. All mod cons, as they say. (British slang, incidentally, is weird.) Anyway—time to start querying Nathan, Janet, Kristin, Jessica, and all the rest. Cast a wide net, and remember: no exclusives!
3. Three months later... you're still querying? Of course you are, unless you're luckier than Malachi Constant. What, did you think this was going to be easy? Keep at it.
4. Three months after that... Hooray! After several form rejections, a few polite refusals on partials, and one or two fulls, you've gotten an offer of representation. (To make this as simple a scenario as possible, let's say this is one of your dream agents and you accept the offer immediately.) Don't start the party just yet, though. Now you've got real work to do.
If you've got representation, you're that much closer to getting published, and so at this point you need to start expanding (or straight-up building) your platform. If you've already got a blog, ramp it up; if you've already got a Twitter account, tweet it up; if you're on Facebook, start making connections like crazy. If not, get going right now. Start playing the networking game. Check Go Daddy to see if your name has already been registered as a domain name. If not, consider buying it. If so, try and figure out a good alternate name. (Hint: http://www.newjohnsmith1-2-3today.info/ is not a good name.)
To be honest, there's no such thing as "too early," but the offer of representation is, in my mind, when things get serious. If you haven't given thought to blogging/Twittering/website-ing/Facebooking/&c, start now.
5. Another three months after that... O frabjous day! Your book has been sold to an editor! You must now do the following:
• Party. Nothing major: you're a working author now. Live it up a little, but do not get outrageously drunk or stab your wife with a penknife. You are not Truman Capote or Norman Mailer (respectively).
• Hit the ground running. Discuss everything with your agent and newfound editor. Ask as many questions as you can think of. If you are, like me, unmarried, childless, and have relatively few obligations outside of your day job, I highly recommend you make promoting yourself and your book your new, all-consuming hobby. Figure out what you're willing to commit to (I recommend as much as you think you can safely handle) and let your agent and editor know you're willing to work hard. If you've got substantial commitments (e.g. sextuplets, reality TV show), find a balance.
• Ramp it up. If you haven't bought that mega sweet domain name yet, do it. Blog about yourself and your book. Tweet about it. Change your latest Facebook employment to "author" and announce your good fortune in your status. Network, network, network.
Let your critique group know. Go to literary events. If you don't already know the booksellers at your local stores (national chains and indies) by their first names, now's the time to start. Aside from the fact that they're most likely wonderful people who will turn out to be excellent friends, they're going to be very helpful later on (see below).
An aside: definitely talk this over with your editor, but if you feel like it's a good idea and your advance is big enough, consider hiring your own publicist. He or she may be able to work wonders for you.
Oh, and yes—if you're not too up on all this computer mumbo-jumbo (although you should be), see if you can get your computer science major nephew (or some similarly inclined relative or friend) to help you out for a nominal fee (or, better yet, for free). If you happen to know a web designer who can make you an awesome website, so much the better. At this point, it's all about who you know. Keep asking yourself that: who do you know who is able and willing to help you?
Now, in case you weren't keeping track, in this oh-so-magical best-case scenario, it's been fifteen months since you finished your novel. You now have representation. Is this unrealistic? Yes, I think, slightly, but don't assume that novel you finished fifteen months ago was your first one, and do assume that you're a talented writer with a good story, and suddenly it's not so far-fetched after all.
Oh—and order business cards. You're an author now.
6. Nine months before on-sale: You might have comp titles already. Ask your agent to check on them for you. If you're neurotic and wealthy enough, pay to track the sales of your comps on BookScan. Discuss potential sales numbers with your agent. Be as realistic as possible. Do not drive your agent insane.
7. Six months before on-sale: You signed your contract long ago and the book has already been through launch meetings over at your publisher's house, meaning that everyone who's going to be involved in selling your book to retailers (marketing, publicity, sales, &c) has known about your book for a few months now. You've got your very own ISBN, retail price, descriptive copy, sell sheets, title information sheets—the works. What's happening now? Well, sales calls. And, if you're lucky, co-op. That means book stores are about to find out all about you.
Remember those friends you made at your local book stores 6+ months ago? Call them. If you haven't already told them about your book, tell them now. Ask if you can do author events, readings, signings, everything, anything. (Discuss this with your agent first.) If you have friends who are established authors, talk to them. See if they'll blurb or promote your book, allow you to guest-blog for them, read with them at area book stores, and so on. You can't do too much of this. You really can't.
Continue to blog, update your website, tweet, guest-blog, &c. The more people hear about you, the better. (Assuming you're always polite and professional—and you are, aren't you? Good.)
8. Three months before on-sale: Keep up your relentless self-promotion, but keep it classy. Follow through on everything. Keep the lines of communication between you, your agent, and your editor open. If you've committed to readings, tours, podcasts, blog posts, e-mail blasts, local radio shows, infomercials, impromptu subway performances, &c—make good on those commitments. If you got your own publicist (see Step #5), he or she will be helping to organize all of these things. Oh, and speaking of organizing, have you scheduled yourself a release party yet?
9. On-sale date: Breathe. Do not check the sales figures yet, they won't be up. Relax. You feel good, you feel great, you feel wonderful. Have that release party you planned three months ago, publish one more blog entry or tweet, and call it a week. You've earned it.
10. One week after on-sale: Your publisher will have your week one sales available. Ask your agent/editor if they can forward them to you. If you're sufficiently neurotic and wealthy (see Step #6), compare these numbers to your BookScan numbers and to the first-week sales of your comp titles. Celebrate or panic accordingly.
11. One month after on-sale: You might have some reviews. If they're positive, blog, tweet, podcast, &c about them. If they're negative, say nothing. Do not try to explain away a bad review in your blog—you're only creating more links to negative press. And for the love of God, do not pull an Alice Hoffman.
12. Three months after on-sale: You're hard at work on your next novel, mate. (This British slang thing is seriously addictive.) Publishing is a business and you're a professional now; celebrate your victories, be gracious about any pitfalls or shortcomings, learn from your mistakes, and keep writing.