If you are a good test taker and read quickly with comprehension, then the best thing you can do is to just be familiar with the organization of the code book. I've passed tests in 4 states and I've never had any formal instruction in the code (or electrical work for that matter). I think I'm a pretty good test taker.
If you aren't a good test taker then one of the prep classes for about $400 would be a good investment.
You should go through all of the examples in the back of the book (calculations) reading all of the referenced sections and know/understand how they came up with the answers.
There is nothing wrong with taking the test to get the feel for it and failing then you know what your getting into for the next one.
Good luck.