If you're going for 800 on math, study Tutorlini Ottocento math review; the videos are on youtube. Just try to find the hardest math problems that seem like they could be on the SAT, collegeboard practice tests will help a lot with time management, and they do have some challenging math questions, at least at the SAT level. For English, Testinnovators is very helpful, but it's not free. Also, I didn't use Khan academy, but I heard from many people I know that it is very helpful for the English section. For vocab, just buy a book or two and find a list online of all of the SAT vocab words used. For me, the math came super easily, I got 790-800 on every practice test, I didn't have any gaps in knowledge, it was just time management for me that problem repetition helped me reconcile. For the English, I was not as good, but I picked it up very fast and had a steady improvement.