130 CARS scorer here. Everyone studies differently, but one thing that helped me was doing Jack Westin's practice CARS (I think some people don't like it, but it helped just to get used to format and get some extra practice). I also did some Kaplan passages from their CARS books. I would say the best help came from really doing the official ACMAS practice exams and CARS practices. Any time I got something wrong, I would reread the passage and analyze what tripped me up and how I should restructure my thinking for next time. Reading books can help, and so can reading a lot of news article to help with reading comprehension.
So...I used to give people the standard advice about reading more widely (periodicals, books, etc.), but I eventually rethought it. The basic issue is this: yes, CARS (generally speaking) favors active readers (and the science sections are similarly much easier for people who have spent a lot of time reading research articles), but the problem is that most people prepare for the MCAT in a pretty short, focused time frame, often with competing life obligations—and randomly reading outside material isn't a very time-effective or efficient way of improving in CARS specifically.
In other words, if you could snap your fingers and retroactively make yourself a philosophy/history/English double major, yeah, that would probably correlate to an easier time on the CARS section of the MCAT. But you've got to work with where you're at now, and you've got to work towards the specific goal of doing well on CARS.
So, as others have said, practice practice practice (using representative materials) and work to understand those materials inside and out. A broad range of third-party materials (exams, passages, etc.) can be helpful for pacing/timing/techniques. Most MCAT courses deal with CARS at least to some extent, and that could be useful too if that's an available option for you. In other words, work to get better at CARS in a specific way.
The final thing I'd note is that CARS isn't just a generic reading comprehension section - it has its own specific structure, logic, and feel. Google "AAMC what's on the MCAT" and you'll find a landing site on the AAMC's page where they provide a lot of information about how they build the exam, including PDFs describing the science and CARS section in a fair amount of detail. It's kind of dry reading, but it's also empowering to read what the test makers themselves directly say about it.
CARS takes time and dedication. Start early and often, going through your method of solving these on paper at first until it becomes faster to shorthand it, until it is faster to do it in your head. Typically I would do one full length practice exam a week with others (so we could review it) and 3 passages per day 5 days a week (so there was one day off per week). Eventually, like everything else that is a skill, it will sink.
David D, MD - USMLE and MCAT Tutor
Med School Tutors
I got 122 my first time not taking it seriously and mistakenly thinking that quantity would be my salvation. I 'did' hundreds of passages, but never really took time to master any approach or analyze then exam. My second time studying I focused more postgame analysis. I actually did way fewer passages my second time around. Rather than try to find new materials (none are that good BTW) I repeated AAMC materials multiple times and really delved into how they asked questions and trying to see a pattern in their answer choices. I was much more active and aggressive in my approach and it paid off. I went up to a 127. You can raise your CARS score, but it takes work you have to be willing to do. NEVER practice CARS when you're fatigued.