Unlike Facebook people don't get on Twitter to find their high school buddies. They get on Twitter to find information, experts, or network with other people in their field of expertise. I don't pretend to know all there is to Twitter, there's a whole aspect of it that I personally "don't get". This is why a lot of people don't use it. There arearticles everywhere on the multiple ways Twitter can be used and companion software for it. (like Tweet Deck, or applications that allow you to post for both Twitter and Facebook at the same time etc...)
As far as getting people to follow you, here's how it's worked for me- I write a blog or an article and then I tweet about it. For instance, I blogged on Whooping Cough and the March of Dimes was on Twitter looking specifically for tweets about whooping cough. They went to my website,
read my blog, started following me and then sent me an email. Likewise, I did a blog about my husband being exposed to Swine Flu at work, the next day The World Health Organization and another organization called H1N1 started following me. It's good form to throw in some more personal remarks about yourself, how your day is going etc.. every once in a while but for the most part people are tweeting links to things they think others will be interested in.
So... if you want to promote your book think about what kind of audience you're trying to reel in. If you're trying to attract other writers find links that other writers will be interested in reading. Find articles on the state of the publishing industry and craft. If your book is about cars tweet information (articles and links) about cars. If you're trying to attract Librarians find articles that Librarians want to read. Who is your target audience? If it's teenagers you're going to have to tweet about things they want to know. At any rate, you can tailor the perfect audience and then start tweeting about your book, link to reviews, your website, whatever.
Also, when you look for people to follow they should be a part of that audience as well. When I search for people to follow I'm generally looking for Health Professionals. There is an application (I wish I could remember the name for it) where you can put keywords in and Twitter will find applicable tweets. So if you're looking for authors find them, follow them, and a lot of them will follow you in return.