It's pretty straightforward. The questions are multiple choice, and if you've read the material and understand what you're reading you won't have any difficulties.
The purpose of the test is primarily to identify areas that you might not have understood properly, so you can review them again with your instructor before becoming certified. If you don't pass, you will review those areas one-on-one with your instructor and retake. At least, that's how I do it ... and how the instructors I worked with as a DM do it. In fact, even if you do pass, a good instructor will discuss the questions you missed to make sure you understand the concepts behind the question.
As instructors, we're far more interested in your in-water skills. The knowledge is important ... but most instructors will work with you on the topics covered in the written test till you understand the material (that's the easy part).
Someone recommended making sure you understand the tables. I agree. Since you're NAUI, I'd recommend focusing on units 4 (Diving Science) and 5 (Decompression). That's the meat of the course, and what students seem to have to work on the hardest.
Sounds to me like you're more prepared than most ...
... Bob (Grateful Diver)