Twitter
TWITTER
Log on to your account. You'll be on your "profile" page. On the upper-righthand corner of the screen, click on the "home" page. Once in the home page, see the search box on the right? This is your new best friend.
Start searching book-related topics. Authors and genres that are similar to yours. The search will spit out people tweeting in real time about these topics. If they look like someone who will like your book, become a follower. Add other writers. Add book reviewers. Add agents. Go to your favorite book blogs and see if they Twitter. I bet they do. Add them.
Meanwhile, update about your book. Give the release date. Talk about the writing process. Review other books you like. Have your own little Twitter niche in the corner of the world that is relevant to books, writing, genre, etc. Talk about your personal life, if you want, sure, but make sure if someone clicks on your profile to check it out you are recognizable as someone with a plan, a specialized topic in the Twitterverse. Nobody wants to add a random Joe who talks about eating turkey sandwiches for lunch.
If you're following the right people and projecting the right attitude on Twitter, you should get a fair amount of people to start following you. Learn how to use Twitter hash tags (#) so you turn up in other people's searches about books and authors.
Start interacting with people. Don't just put your tweets out there and forget about it. Seek out people and have conversations with them. Respond to people who have conversations with you. The more you interact with your followers, the more people on Twitter will see you and maybe want to follow you as well.
Additionally - do you have spare copies of the book? Once you have a decent handful of followers - give some signed copies away. Ask trivia questions or come up with some other fun contests. Tell people that if they retweet the release date of your book, they'll be entered to win a free copy. Whatever. It's exposure. And follow through with whatever you promise to give away.
You can be extremely creative with Twitter in terms of getting people to interact with you, but again, you have build up a lot of it on your own. Add a Twitter banner to your website. Google ways to find more followers. Don't under-tweet, but don't saturate the web, either. Find a nice balance. Hook your Twitter account up to your Facebook page. Apply many of the same ideas from Twitter to Facebook.