If you're using Twitter and Facebook to promote your blog or your book or some other business venture, I suggest you read Zarrella's Hierarchy of Contagiousness: The science, design, and engineering of contagious ideas by Dan Zarrella.
In just 64 easy to read pages, Zarrella debunks many social media myths, and he uses data from his own studies to show you how often to tweet or update your Facebook page and much more. Did you know there are precise days of the week and perfect times of the day to get retweeted? How about the best time of the day to post on your blog or send an important e-mail?
You'll learn the best and worst words to use in your tweets, the kinds of information people are hungry for, and why you want to use "you" instead of "I" in your communications.
While you're at it, you may want to check out Zarrella's website/blog for more ideas on maximizing your time on social media.