Whatever you do, just do something that is not overwhelming to ensure you stay focused and stick to the plan. Don't go out and buy a bagillion study guides, its overwhelming and you will feel like you don't know where to start. I suggest picking one company, create a gameplan, and just stick to it. This is from personal experience that I know an overwhelming amount of study materials can cause you to shut down. I am using EK's Audio Osmosis, and going track by track (about 2mins at a time), writing my own detailed notes, and then reviewing them each night. It has been effective and I do about 2hrs per day, 10hrs a week of listening to AO.