When there’s only a week left before the SAT, is there anything I can do to prepare?
The short answer is, unfortunately, not much. Of course it all depends on where you’re starting and what score you want to get, but in my experience, very few students make significant gains without several months of preparation. Then again, there are a few things you can do for the math and the writing to improve your score in a short amount of time.
On math, you can learn about throwing in numbers. The algebra required on harder math questions can be very difficult for many students. However, these same questions can be solved rather painlessly and quickly by substituting numbers for the variables, and doing simple arithmetic using your calculator. Knowing this fact and using it to your advantage can account for a small jump in a short time.
On the writing, just reviewing the grammar rules ETS likes to test (especially the most common ones- those involving verbs and pronouns) can help tack points onto your score.
As for the critical reading, I’m truly sorry, but there’s very little you can do in a week that will directly impact your critical reading score. Of course, you can take a few practice sections to familiarize yourself with the questions and types of passages, but without a long term vocabulary plan and extensive practice, the critical reading score is very difficult to move.
If you’re set on trying to prepare with only a week left, what I would recommend is taking one (or a few, if you have the time) of the College Board’s official tests; there are several available for free online, many more available for purchase (ten online, and another ten in the SAT Study Guide, or the “Blue Book”). At the very least, taking a practice test or two will get you more familiar with the test and its timing, and this may boost your confidence on test day.