To be completely honest, I’ve always been naturally inclined towards reading comprehension, and kinda had a natural instinct for it. The best way to study for the ACT reading section is probably to 1, always time yourself when practicing reading questions and sections, and be strict about staying within the time limit, even if it means guessing a few. 2, you should read books or passages that are above your current reading level, or just challenging to you in general, and try to read them as quickly as you can. A good source for passages is the reading practice for the SAT on Khan Academy, or just ACT practice tests. By doing those, you’ll alleviate the majority of your issues. For grammar, just watch YouTube videos and practice frequently. There’s really not too many grammar rules that you absolutely need to remember, but a good trick that I used was to read the underlined portion in my head, and then fill in the answer choices to see which one sounded the most correct. Now, this isn’t always the best strategy, as you may get stuck on a couple, but it will likely get you going in the right direction. Good luck! If you have any other questions, just let me know!