If you're promoting a book or blog, be sure to include the name of your book(s) and website in your Twitter bio that goes beside your photo. You have about 160 characters to write something to introduce yourself. Here's my Twitter bio as an example:
In the website space in "profile settings" I inserted the link to where readers can buy my book: http://store.samhainpublishing.com/dead-winter-p-6507.html . This goes underneath your bio. You want to include your website in your bio, because that gets emailed directly to people every time you follow someone, and it gives people the opportunity to click on your website link right from their email. The designated website space below the bio allows you to post a second link to a blog, Facebook page, or Amazon page of your book.
Now that your bio is set up to best promote your book and website(s), you want to search for people who are most likely to read what you write. There are a number of ways you can search Twitter for readers that fit your demographic. I will cover many of them in this series of blog posts. 
Today I'm focused on searching for key words in the Twitter search. If there's a certain author in the same genre that you write, then do a search on the author's name. This brings up a list of everyone talking about this author and their books. Those tweeters would be good ones to follow because they have an affinity for your niche. For my genre, I might do a search for a popular horror author or key words like zombies, werewolves, ghosts, vampires, supernatural, or horror novels to find my audience. 
This will take me to a results page with people talking about horror novels. I scan the tweets on this search list and read not only their tweets, but their bios as well. I look for key words in their bios like: avid reader, love reading, book junkie, love horror, or love Stephen King. These are the booklovers that I choose to connect with.
If I were a cookbook author, I'd search for people talking about recipes. If I were promoting a health book or diet book or a how-to book, I'd search for people tweeting about topics that matched my subject matter. When you follow them, they are now aware that you have a book that matches their interest. You've now introduced yourself, your book title, and your website to a person who has a high-probablity of buying your book. If they follow you back (and many of them do with gratitude and enthusiasm), you can message them with a "thank you for following" and start a dialogue. In social media, selling books is about building relationships with people who share your common interests. The more time you spend getting to know readers and letting them get to know you, the more likely you are going to sell books. What's phenomenal about Twitter is that your fans that you connect with will eventually become your promoters, as well. They will tweet about your books with high praise and spread the word, attracting you more fans and book sales.
I have more Twitter tips to come ... to stay tuned, subscribe to this blog.
My author website: http://www.brianmoreland.com/
Here are some tips on how to use Twitter to market your books and blogs and build your audience. For those who are new to Twitter, it's a social media site where you set up a profile and post short messages about what you're doing. These messages are called "tweets." People from all around the world can "follow" you and read every message that you post. Just about every celebrity imaginable now uses Twitter to give their fans a personal connection. Twitter is also great for authors connecting with their readers. This is a goldmine for marketing books and blogs.