For students that typically perform poorly on tests--specifically standardized tests--one of the best methods to prepare for the SAT is with a tutor. A tutor will work with you one-on-one to help you prepare, and even relax, for the test. Many students learn better with a tutor because they feel more comfortable answering and asking questions, and they are given individualized attention. You can find an SAT tutor at different local learning centers as well as by asking the teachers in your own school, as many teachers tutor on the side for extra money.
There are many intelligent students who simply don't do well on standardized tests. If you're one of those students, think about taking SAT/ACT classes. These classes will help you take standardized tests better with tips and advice from a classroom instructor. For example, you need to know how blank answers are counted for. On the SATs, leaving an answer blank doesn't necessarily count as a wrong answer. These tips will help you take your test more confidently as well as prepare you for college, where many tests are standardized. You can typically find open SAT classes at a local community college or even at your high school.
For the subjects that you struggle in, take practice tests whenever you can. Talk to your teachers, as most teachers know what kind of questions, problems or literature will be covered on the SAT so they can prepare you in the classroom. By talking to your teachers, they may be able to help you understand the material better or help design practice tests for you. This is especially useful for subjects like math, where you don't just have to know the answer but you have to prove you know how to get the answer.