Hi, Missy,
Beside Liburdi's book, I like Martin Edge's The Underwater Photographer. It is not too advanced and the photos are positively inspirational.
Also, I do not know where you live, but if you are in Southern California, you can visit the master, himself: Joe Liburdi has a dive shop at 15315 Culver Drive, Irvine, California--he even has a web site:
http://www.liburdiscuba.com.
Joe is very personable and will talk to all who approach.
Finally, about photos underwater there is one paramount rule: reduce the column of water between camera and subject. In simple English, get close!
This advice is somewhat frustrating since you will discover that fish have a "safety zone" and each species is different. What that means is you can only get so close and the fish will swim or dart away. As your diving skills improve you will find that you can get closer because you are less disruptive. Oh yes, "chasing" fish burns up a lot of air and usually does not work; they can swim faster than we can!
There is a school that says start with Macro because you can take close-ups of coral, nudibrancs, sponges, clams, etc. and they don't move! One of my favorite photos that I took is a close-up of some perfectly formed maze coral...a pretty pattern and nice color.
Have fun with your camera!
Joewr