Use the SSAT website and go to the main page. Each day they have a test question in the lower right hand corner that you can answer. You will get immediate feedback as to whether or not you got the question right.
Spend the money and buy the study guide. This will not only have the kind of questions you'll find on the test, it will also give you a general idea of how difficult the test might be for you.
Network with friends. Once you have the study guide, ask around and see who you know that has taken, or will soon take, the test. Practice asking each other questions so you can benefit from the study time together.
Search the web for practice test sites. A few provide the test and a study guide free of charge. Your answers are instantly evaluated, and best of all, there is no charge to take the practice test.
Consider taking an online preparatory class before the SSAT test. This will give you practice and familiarity with the information and help your confidence as well.