A lot of it depends on the type of book it is as well as the target audience. Most authors start off with trying to generate as much (free) publicity as possible starting with sending books out to be reviewed (magazines, newspapers, independent reviewers such as Midwest Book Review)
You may consider joining the Kindle Select Program where you offer your book as a free download for 5 promotional days. The ideal is that many people will download it and spread the word to their friends to buy it.
Submit your book to reputable book award contests such as ForeWord Reviews Book of the Year Award, Independent Publishers Awards IPPY, and Readers Favorite. (note there are fees to enter your book into these contests)
Having a press release can also generate buzz but it requires a small investment.
Sign up to receive email alerts from HARO (Help A Reporter Out) and Radioguestlist.com These sites are designed to help media people and experts/authors/entertainers and others to connect. A lot of them will be POD cast radio shows but nonetheless it's still a way to promote your book if it is related to their topic.
You can also check out meetup.com to find book clubs where you might offer to come and speak.
If your book is a self-help book you can create a workshop/seminar around it or create a class for community colleges continuing education department. You can also create online classes for ed2go.com or learning annex.
Be an exhibitor at a trade show, book fair, or industry related show.
Offer to do a program/class, or hold a meeting in your local public library on something related to your book. Libraries and local community venues are always looking to fill their calendars.
Write blogs/hubs, use twitter, facebook, your own website, linkedin, and network with other authors. Below are some links for stuff related to my book.
http://www.amazon.com/Cat-Wont-Bark-Relationship-E... (note: Editorial reviews) - Best of luck!