I am prepping for this exam in the following manner: looked at the credentialing site and took the practice tests, reviewed the reference list (quite lengthy......26 references total) and ordered a few books from amazon.com to study with. Best books so far have been: Core Curriculum for Pain Management Nursing (ASPN), Pain Assessment and Pharmacological Management (Pasero and McCaffery). Many of the references are online and you can download them. There is a test content outline, summarizing all the content on exam and what percentage of each topic is included. I began studying in January and plan to take exam by summer. There is lots of good info on the credentialing site, but I am sure you have seen it. I think there is a review course, with modules online available for purchase. I wanted to dig all the info out for myself and take my time.
GOOD LUCK ON EXAM