Most efficient method is subjective based on the individual in question. Most individuals, I would think will tell someone first hand knowledge, then understanding the concepts involved in each of the domains on the
Official practice exam questions (with the understanding that the intent is to get you to focus on content or contextual meaning of the questions). There is no hidden secret trick other than to know through exposure or have understood the contextual information provided through study of areas one felt they were lacking strength of knowledge in. There is no one solution that will provide all the information in one location which could be asked on the exam. Hence, "Inch deep, mile wide." I know that this is not the answer you are looking for and it may not actually have provided you with any information you did not already know. However, in all fairness, many have realized to late that just knowing what was in one book or by watching one set of training videos was not enough to pass the exam. One needs to have a broad knowledge base from which to pull all the possible information, (NIST SP, ISOs, Different frameworks (example: Zachman or OGAF), most of these should have been discussed in your studies, however, don't always think that the questions will directly address items by name, they may be addressed by concept. If someone tells you the answer then you should know the question.
Positive thoughts and wishes are with you
