This past summer, I attended the SAT prep class Dr. Li's. I had done next to no research on the SAT before, so truthfully I didn't know what to expect. Once we started doing practice problems, I admit, I was a bit unnerved by how many I was getting wrong. Reading comprehension was just reading comprehension, so why was I making so many mistakes? Having taken the test two times now, what's become clear to me is that SAT is not only about your overall academic ability but also (and perhaps more importantly) how well you can cater to what Collegeboard wants of you. The SAT uses and reuses specific types of questions, and having experience in dealing with those questions in a timed environment is key. Especially with reading comprehension, it's oftentimes better not to overthink a question and just consider, for a moment, what answer choice Collegeboard expects you to pick. This becomes almost instinctive once you've done packets after packets of practice.
With the writing/grammar section, it's important to take a step back and realize that, even as native English speakers, our grammar is oftentimes plainly wrong. I recall several times during Dr. Thompson's grammar class in which I realized, for example, that I use "try and" over "try to" all the time. And once this fact was made evident to me, my mistake was clear as day. Once again, practice, practice and practice is key in this section.
In math, the greatest advice I can give is to check your answers. Yes, the math section is comparatively very easy compared to what you learn in school, but it's also lengthy. The more questions, the more room for mistakes, and as such check, check and check your answers. What I really liked about Dr. Li's program in this area is that it took from previous SAT questions and modified them in a way that made them more challenging. Too much is always better than too little in your preparation for any test.
Finally, the essay. With the essay, it's absolutely, absolutely imperative that you pay attention to what the teacher tells you regarding what graders are looking for. After all, the SAT grading turnaround is absolutely shocking: while I don't know the exact numbers, I'm sure thousands of kids take the SAT each time it's available, and graders manage to grade all the essays within 2 or 3 weeks. You know then, that they don't have time to analyze in depth what each person is trying to express in their essay. The SAT essay is not a complex piece of writing, and it frankly leaves very little room for originality, but this can be played to your advantage. Follow the formula the teachers at Dr. Li give you, because it works--you can worry about creativity and writer integrity on more important pieces of writing.
With all this in mind, I took the SAT, and I managed to score a 1600 and a 23/24. A very big thanks to Dr. Li and everyone who taught me :)