Alan Rinzler wrote a great article on how authors can best utilize Twitter.
He suggests that writers should use their real names (the one they write under) because your name is your brand.
Know your audience, and build a following by finding and following people who are interested in your topic through Google's book blogger search and with http://www.twellow.com which is like a yellow pages for Twitter. Also, @GalleyCat on Twitter has compiled lists of useful people to follow, including book reviewers.
Putting people into lists on Twitter lets you see the most recent posts by people on that list. Follow them, and they might follow you. Start Tweeting, and make sure your posts are original, funny, timely, or informative: the kind of stuff others may retweet. Retweet things you find interesting. Provide content about your topic, area of expertise, or if you write fiction, "a character, scene or situation you're working on." I would also add that you should ask questions. It's a good way to meet people in real life, so why wouldn't it work online too?
Link back to your blog, Tumblr page, website, Facebook, and include your Twitter name in your email signature, on your websites and blogs and so on. Put it in the back of your book. And after a while, mention that your book is available and link to where people can read chapters or buy it. Don't try to sell your book. Instead, simply try to provide useful content to others.
Great article! http://www.alanrinzler.com/blog/2011/03/20/strategic-tweeting-for-authors/