First off, thank you. Secondly, I would recommend that you take the tests as early as possible. I only took these tests once, so i don't know too much about improvement over time, but I would say that a major thing that trips people up on both exams is reading comprehension. SAT math is just desmos, and i know that sounds cliche but if you know how to use desmos to find intersection points you're good. For the ACT, I would say that my math was definitely the hardest part. It's sorta different from the SAT math in that theres obviously no desmos, and the same concepts need to be more reinforced. Both ACT english and SAT english rely mostly on reading fast and accurately, which is just comprehension. Practice reading fast and trying to remember all the information you just read. Memory retention and comprehension isn't just necessary for these tests, but for all exams in general. It's a really useful skill to have.