There're quite a lot of good books you can start with, depending on your background. Generally most books that touch on trading in general will apply for CFDs as well. If you're totally new, you might also want to pick a book that covers more than just trading methods and analysis to include topics like risk management, position sizing ...etc.
The Internet has a load of free stuff you should check out first... sites like Investopaedia, Babypips.com all have great stuff to start you off. Once you get acquainted enough, I would suggest New Trading Systems and Methods by Perry Kaufman.