People have different study styles and there is not only way to study effectively. Like others mentioned above, you just have to find what works best for you.
In my case, I always had good ITE scores, so that was a plus. I bought the med study books but only went over like 10% of it, because I found it too dense and time consuming. I tried watching videos, but they were boring and I couldn't focus. So I decided I was going to do ONLY questions and flashcards. No study book, no videos, no study groups, etc. I did PREPs 2015-2020 ( 2019 and 2020 I did twice). I finished all Medstudy questions once and did the wrong ones again. For PREP, I started with 65% ish in1st/2nd year, by 3rd year I was doing around 70-72%. First pass on medstudy 70-75%, second pass on the wrong ones around 75% as well. Medstudy Flashcards for the topics I had trouble with. Also, I did the 2019 self assessment from the ABP website, which I passed with 78% one week before the exam.
It might seem a lot of questions (and yes, it was), but it was only possible because 1) I started early - by the beginning of 2nd year I had already finished PREPs 2015 and 16; 2) I did questions every single day - even if it was a couple questions when I was in the bathroom, almost no day passed where I didn't do anything and 3) I did not lose time with study books, which for me were just too boring and time consuming. I know so many people that dislike PREP but, even though the questions are long and not like the real deal, PREP offers huge explanations about every question and, if you read them well, in the end of ~3 years of PREP, you went over a lot of information. And medstudy questions were great for reinforcing what you knew and pointing out which topics would need a little more attention. So they were both worth doing IMO.
Anyways, just wanted to share here my experience, for people to see that there are many ways to prepare for this exam and get a good score! I passed the exam with a score well above the mean, with
no text books,
just questions.
Good luck for those who will take the exam in 2021!