I realized in yesterday's post about Twitter, I skipped over one of the benefits of having a Twitter account: If you have something to say, it gives you a place to say it. Blogs do that, too, of course, but with Twitter it's easier to reach people you don't already know. And it works best if the thing you're saying is not just, "Buy my book," but rather something of general interest.
As a Kindle owner, I like to announce when books I've been waiting for come out on Kindle. Or if I've read a book I really like, I tweet about that, with Kindle availability only a sideline to the tweet.
The stolen elections in Iran are an example of Twitter's bully pulpit in its extreme form, but smaller scale events and platforms get exposure, too. And with a 140-character limit to tweets, people have to come to the point quickly. You can, with clever abbreviations and some grammatic license, review a book or a movie in 140 characters.
Express yourself to the world!