How do I get copyrights to a book I'm writing so I can promote it before it's released?

[Gemi]

Your story is already copyrighted by law as soon as it's written. But if you want formal protection, register with the copyright office.

U.S. copyright office: http://www.copyright.gov/fls/fl109.html

Take note that self publishing impacts potential future contracts. Most publishers won't purchase copyrights unless it's the first serial copyright of the actual story. So keep that in mind if you intend to gain the interest of a legitimate publisher.