On Twitter, it's better to treat it as a way to connect with people, and to only use it occassionally as a promotion tool. Because I write for children, I follow teachers and librarians and talk about children's books (other than my own most of the time) and a little about my life and writing, and also about things that interest me, so I end up retweeting things about science and animals. To find people to follow, search for some key words relating to what you write and see if you can find people that way.
There are also tweetchats on a variety of different writing-related subjects. I clicked on your amazon link and see you write paranormal romance, right? There is probably a weekly tweetchat about that.
Do you know about hashtags? Here's a link if you don't:
http://www.searchenginejournal.com/twitter-hashtags/9419/
I use hashtags on some of my tweets if I think the content will be interesting to people I don't follow, but yet have an interest in a particular subject. For example, I add the hashtag #homeschool to tweets about resources that might be useful to homeschoolers. Since you have a goodreads giveaway going on, you can add the hashtag #giveaway to a tweet with a link to it.
Twitter is time-consuming though. I've been staying away from it for now because I'm trying to concentrate on writing and research.