John Kremer says don't write a book unless you're committed to three years of marketing. Of course, this doesn't apply if you are J.K. Rowling.
Marketing is a vast subject, so avail yourself to resources. I've found Kremer's 1001 Ways to Market Your Book helpful. Tom and Marilyn Ross' book, The Complete Guide to Self Publishing, has great marketing content. A Novel Idea, a book I purchased at Conference has a great section on Networking and Marketing.
Marketing boils down to promotion and distribution. They can happen together, but authors must get the 'word' out about their books and must make sure their product is available.
The first question an author should ask is "Who will buy my book?" You need an answer or you need to do research.
Marketing in its lowest common denominator is about creating relationships, which means making friends. Friends tell friends about books they have liked. This powerful tool is called viral marketing and is one of your best approaches. Visibility is still critical for your book; however, you must make it happen. Your nation-wide marketing plan is all about visibility.
Many publishers, definitely the small press ones and even others as well, want the author to have a national marketing plan. Of course, you make a splash locally, but one does run out of friends and family. That said, it's still good to make a big splash in a little pond. Work your home front for all it's worth.
Nation wide, things like reviews and endorsements, blog/tv/radio interviews, press releases, personal web sites and blogs, media kits, book tours or signings and speaking engagements become important. A lot of buzz can be created on your social network sites, your blog and website.
If arrangements with your publisher are permissible, always carry copies of your book with you for when opportunities present. Keep a special bag filled with your book in your car. Pack some in your suitcase when traveling.
Plan on dispensing promotional copies. Ask your publisher for as many as possible. Negotiate this if you can. You may generally buy from your publisher at a discount rate.
One authority says liberally 'giving away' your book to friends and family lessens its value. Not an easy call here. Maybe 'liberal' is the key word.
The first six months are your prime times to market. A new book is still a new book for six months. Your book will continue to sell after six months, but maybe slower.
Some have a passion for marketing; some hate it, but writing your best possible novel is only the first step. Then, there's more work, but it's worth the effort.
Seize not only the day, but seize the buyer too with your marketing pizazz! This has been my experience in marketing my nonfiction book. Tell us what has worked for you.