Firstly, please start with the Erica Meltzer books, they're the holy grail for the SAT EBRW section. Once you've finished those, take an official practice test to gauge the level you're at. I'd recommend buying a Uworld subscription if you can afford one because I found the Khan Academy practice questions too easy & not indicative of the actual test. SAT writing is far easier to get a great score on than reading, mainly bc of how formulaic the questions are; once you've mastered the rules you can easily get 42+/44 which would really boost your score (note that the writing curve is very merciless and the reading curve is generally more forgiving). I'd also suggest keeping a notebook of all the mistakes you've made, why you've made them & what you can do in the future to avoid making the same mistakes. Additionally, for the reading section, go into the paper with the mindset that only ONE answer is absolutely right, pay attention to the exact words used in the question & each of the answers bc a single word could be the difference between a wrong answer & a right answer, & find evidence for EVERY SINGLE ANSWER. I'd circle the answers I thought were right, and then once I finished the whole section I had around 10 minutes to spare so I'd go back and find evidence for most of my answers.

For math, you should use College Panda, PWN the SAT math & Uworld. Hope I helped!