When you begin studying for the SAT, it's important to get a baseline for where you are. Start off by doing several practice tests from Princeton Review, Kaplan, Barron, etc. Save the official CollegeBoard practice tests till the end since that is the closest sample you'll have of what the real test will be like.
Princeton Review and Kaplan both offer full (and free!) in person sample tests that are designed to be just like the real thing. They're really good for practicing taking the full 4 hour test in one go and making sure you can perform optimally throughout that period. Test taking skills are a critical part of the process and knowing how to manage your time is something you'll only learn by practicing.