There are many different types of study guide books for the SAT. The College Board, the company that created the test, publishes its own book called the "Official SAT Study Guide" which is currently in its second edition. There are also books from The Princeton Review and Kaplan Test Prep that are excellent studying resources.
Taking a practice test is one of the best ways to ensure your success when taking the SAT. Practice tests make great study materials because they give you an idea of what you can expect on test day. If you know what to expect, you will be less likely to make silly errors because of something you didn't understand. A practice test is also a great study material when taken in conditions that are similar to the ones you will experience during the test itself. Practice in a quiet room and time yourself.
Sample questions, which can be found in many study books or on The College Board website also make great study tools. If you don't have time to take a complete practice test, consider practicing on some sample questions. These sample questions will give you a good idea of exactly the type of wording you will find on the actual SAT test.
Many high schools offer their students free SAT prep courses, but some schools don't. Some students may wish to take SAT classes from the comfort of their own home instead of at school or in addition to the classes they are already taking in a classroom. The online preparation classes make great study tools because the skilled instructors understand the inner workings of the SAT and can provide individualized materials to help each student reach their full potential.