The “Body of Knowledge” for each certification specifically identifies the areas in the codes and standards referenced that you should be familiar with. In some cases specific paragraphs are identified in at the end of “knowledge statements” in the documents. The “Body of Knowledge” is free and you may obtain one by calling API at 202-682-8064 or downloading one at http://www.api.org/products-and-services/individual-certification-programs/programs. Go to the Select Program drop down menu, select program, then go to Exam Info. Read all the areas of the codes noted in the Body of Knowledge at least once.
The Body of Knowledge also has a section on what NOT to study. Read this too so you do not waste time studying information that you will not be tested on.
The questions for the exam are written by volunteers and, like all volunteer projects, are probably done the night before they are due. Read the documents as though you are looking for some nice facts to make multiple choice questions out of and highlight them. Memorize that information. Use the information in different contexts so you develop a complete understanding.