The SAT has recently changed in a few key ways. The wonderful thing about this is that the SAT now tests concepts much more closely related to what students actually learn in high school. The unfortunate thing is that it is much more difficult to prep for it now.
The SAT currently tests Writing, Reading, and Mathematics. Each of these sections has a different preparatory strategy.
The writing test includes both a 25 minute essay and a grammar section. I strongly recommend getting a copy of a sample essay and practicing. You should be familiar with the format and timeframe of the essay before you sit down to take the test. Similarly, practicing grammar questions will make the test much easier, as only a few grammar rules are tested on a consistent basis.
For the new reading section, which is very challenging, the best strategy is simply to read widely. Studying targeted vocabulary will help but not as much as it once did. The test is almost entirely reading comprehension now, with a focus on inference and interpretive questions.
Finally, for math, get your hands on a good prep book that lists the concepts and make sure you review your fundamentals. The test covers geometry, algebra 1 and algebra 2, so if you’ve taken math classes beyond that, you are likely to have forgotten some of the basics. Concepts like ratios, proportions, and averages come up very frequently.