Students doing PSAT or SAT practice tests for the first time may immediately realize that these tests are quite different from most of the tests given at schools. But they should realize that although there are always a few relatively hard and trick questions, most of the questions test the basic math knowledge and skills, so some of the questions are not as hard as some competition questions given to middle school students.
One should start with one or two good SAT prep books, instead of directly going to a test prep course. When the student has reviewed all the materials, and done all the practice tests, and can score at least 80 or 90% on the practice tests, but still want to get to the next level of targeting full scores or close to full scores, then they should take some test prep courses with good instructors, or take private tutoring.
The SAT test prep can and should be started early. I know a number of my students who have taken the SAT when they were/are at the 7th or 8th grades, and a number of them have scored over 700 in Math, much better than the national average of all test takers, most of whom are in high schools.
I have used a few books, and could recommend the following. All of them are available from www.Amazon.com. Click any title to find more details about that book.
1. The Official SAT Study Guide.
2. 11 Practice Tests for the SAT and PSAT, 2008.
3. Cracking the SAT, 2008 Edition.
4. Barron's SAT 2400: Aiming for the Perfect Score
5. How to Prepare for the SAT, 2008
Click this link to find more SAT books at Amazon.