It is understandable that you are nervous about taking a certification exam.  These exams are not easy. But preparing wisely will help reduce some of your anxiety and allow you to concentrate on the important stuff, like the correct answers!

The first preparation step is to identify your learning style.  If you are not sure there are online assessments to help you.

http://ttc.coe.uga.edu/surveys/disclaimer.html?
LearningStyleInv.html

http://crse002.lsu.edu/lac.nsf/guest-diagnosticframe

Once you know how you learn best, then tailor the preparation around that fact. 

Preparing for the test:

• Identify the types of activities that help you retain and understand the material.

Do you learn best by listening?

• Then get an audio review tape or have someone read sections in the book aloud. Or organize a study group to discuss the concepts.

Do you learn best by reading and note taking?

• Then create outlines and flash cards.  Take lots of notes, then synthesize them down into an outline or draw out a concept or mind map. Create study guides, ie. flash cards, mnemonics, course summaries, etc.

Do you learn best by doing an activity? 

• Then create a presentation on the areas that you are struggling with, go to a job site where the concepts are being used, build a diorama or present the material to someone else.