A good first step is to spend lots of time on the forums and see what kind of questions people are asking. Answer the questions you can answer, learn from the questions you can't answer.
An intermediate step is to learn about virtualization. Create virtual machine installs of Debian, CentOS, and Slackware (for starters). Build a network between all these virtual machines. Learn about file sharing, web services, backups, security, etc. If you have more than one computer, set up a physical network, too.
All of the information you need is out there on the web. Linux is very well documented! If you're looking for an actual physical book geared toward passing an exam, Michael Jang's Red Hat prep guide is highly regarded.
Also don't neglect your Windows skills! Don't limit yourself to just Linux administration, learn about Windows stuff too. Get your Linux and Windows machines talking to each other.
A final thought, most employers aren't interested in a list of books you read. Times are tough even for experienced job-seekers. A little experience is better than no experience. Look for open-source projects that need volunteers. Offer your services to schools, social service, small business. Look for short-term, easy projects on Craigslist, Elance, Odesk, etc. Employers want to hear "This is what I've DONE in the past, this is what I can DO for you in the future!"
Good luck, check back in often and let us know how it's going!
