The world of Web 2.0 offers new and uncharted territory for authors looking to promote their books. It’s the great cyber frontier brimming with new realms of discovery, new possibilities for interactivity, and new approaches for defining publicity and getting the attention that sells books.

Let me be blunt: it’s not enough for an author or publisher to simply post a website and expect that “they will come.” With around 3.13 billion books sold last year – 411, 422 titles released in 2007 alone — it’s crucial for an author to set themselves and their books apart from the masses.

It’s great to sell books at book signings and other in-person events, but they are by nature limited to the eyeballs in attendance, and those eyeballs already knew enough about you to want to show up. What about those who would have bought your book if they had only heard of you? How do you reach this majority?

This is where you can tap into the enormous power of social network marketing. By strategically engaging with the various social media sites, you can drive heavy web traffic to your site. A well-designed site should see high conversion rates from the traffic, particularly since much of it will be pre-qualified. Which means more book sales for you. See where I’m going with this?

Here are five reasons why authors should use social media networks as part of their professional publicity campaigns:

See high search engine rankings. Content posted to social network sites gets high search engine rankings. Check for yourself: Google any term and count how many wikis, blogs, Squidoo lenses, Hubpages, and other social media sites appear on the first page of rankings alone. How do you join them? Participate by posting solid information on content sharing sites like Squidoo.com or Hubpages.com (but it shouldn’t be about your book).

Get incoming links. Google loves incoming links. Just as publicity in the form of a magazine article is seen as an implied endorsement, links coming from other sites also offer credibility, particularly to search engines. Plant keyword-based links to your site inside how-to articles you post on ezinearticles.com, for example, and every time that article gets picked up and posted somewhere you get more incoming links.

Find your fans. Or rather, help your fans to find you by having a presence where they gather. Even better, help those potential-fans-who-don’t-even-know-to-look-for-you to find you. How do you do this? Mine your common interests and show yourself beyond just the author of a book. If you write historical novels set in Bavaria, for example, go ahead and post a slide show on Flickr.com of the photos of Bavarian castles that you took on your last research trip. Other people who like Bavarian castles will find your photos and end up at your website. Maybe they’ll even buy a book.

Expand beyond a “book”. Offer ways for fans and potential fans to connect with you in other mediums, like videos or podcasts. This gives even non-book-readers ways to learn about you and what you have to offer. To support my cookbook, I offer a series of free 3-minute cooking demonstrations that are hosted on YouTube.com. It’s a great way for visual learners to identify with me, my cooking method, and of course, my cookbook.

Drive traffic to your website. Even if you don’t offer e-commerce on your own site, you must at least refer buyers to where they can purchase your book. You do have a website, don’t you? ‘Nuff said.

But be careful out there! Do it the wrong way and you could find yourself booted out of the community or worse. Members of online communities don’t like to be marketed to, so leave the marketing language at home and use a little more creativity in your approach. While Web 2.0 is still the wild west in many ways, there are definite codes of conduct and moral standards you would be wise to follow.

Most importantly, don’t forget to have fun! The new web offers so much to explore and learn, and so many ways to connect with others that you might even get distracted from writing books!