I had same dilemma exactly 1 week about about how to start it. But now I can say that at least I have started. I started reading SC theory from PR verbal workout
book and then moved on to solving OG questions. For RC you have to chose your own set of rules about how you are going to attack the passages from OG, so start doing them and see which method suits you best. For CR "Powerprep Logical Reasoning Bible" is excellent book. Finish this book first and then move onto OG, but do remember that this book itself is over 500 pages, so do not try to finish it in within a week. You need to understand the concepts in this book so take good time may be atleast 15 days or so. But I will say before starting RC do finish up first four chapters of "Powerprep Logical Reasoning Bible".