For the math portion, the thing that helped me the most was doing a lot of practice problems-- I mean A LOT! The SAT has so many nuances that can’t be adequately described in words, but rather they are best learned through experience that one can only attain through a multitude of practice problems. After I finished the 8 practice tests, I felt that I needed more practice, and as such I went out and looked for some other source to practice with. I found UWorld on Reddit with a free trial code and I found like 500 SAT Math problems that were almost the same as the 8 practice tests. So, I would recommend that you look through Reddit to find the UWorld free trial code (if you can’t find it just message me and I will find it for you). UWorld and the 8 practice tests are all you need to achieve a 750+ on the SAT. After a 750-770, it is really about luck and the test that you are given honestly.
Source: 790 SAT Math. 760 PSAT Math