I'm not trying to sound negative or mean in any way, but a lot of being a tech has to come from experience. I'm sure there are books that could help you learn about various aspects of the job, but they're no substitute for physically holding a mean cat while the vet is trying to draw blood from the jugular (for example). My first few months as a tech, I felt like an idiot about 90% of the time. But stick with it, and you'll learn a lot of valuable stuff! I've been a tech for about 6 years, part time, and last week was the first time I've taken an X-ray, without any help from the doctor with technique and positioning, where it actually turned out well! So what I'm saying is, it can be a pretty slow learning process, so just have fun with it.
One thing I would recommend, though (although they're a bit pricey, but I got mine on sale), if you're really interested in what's going on around you, is to get a Merck Veterinary Manual. Every time I hear the doctor talk about something and I don't know what it is, I jot it down on a piece of paper and look it up when I get home. I know, I'm a HUGE dork.
I've also been kind of studying it lately in preparation for my interviews. If you don't want to get the Merck, there are probably textbooks floating around the clinic that you can read during your breaks, and the internet probably has some places where you could look stuff up, too.
See if there are any books lying around at the clinic where you work that may help you. There's one where I work called the Veterinary Technician's Clinical Textbook, or something like that, and I've looked things up in it a couple of times. Good luck and don't get discouraged! Just hang in there and it'll all be worth it.
