I have no idea how I learned back in grade school. I was pretty much the full-time daydreamer who managed to learn anyway. My poor parents had no idea what to do with me. Neither did my teachers. But I muddled through, often getting good grades, but poor at things that took lots of boring repetition. Mom always said that I didn't apply myself or I wasn't living up to my potential.
Much of my issues revolved around skills. To make my brain learn, I could not take the skills that others used. I could organize myself, but after a few weeks I stopped doing that and had to start over. "Organize" only works if that type of organizing works for you. If it does nothing for you, then organizing is just an empty exercise in feeling good. (If you go to a professional organizer, they will actually have you NOT do many organizing things, as most people confuse organizing with storage.)
I also could not CRAM. If you put all my notes in front of me, I'd be bored of them in five minutes. My brain just freezes up or goes dead when I read things multiple times. "All this goes into short term memory and will be gone by morning! La la la."
I really need to learn as I go. Any other method is just unworkable, my brain either wanding off or just plain turning off from the tedium. That got me through high school. It worked well until senior year when the crunchier classes began demanding more.
In college, I really worked out my modern study habits. Most importantly, I need to read before class. I need to read when I don't know what I will be reading. That forces me to pay attention. (If I already know what I'm reading, I'll skim, and that's not good.) Going to class, I get verbal reinforcement of what I read, reinforcement on what is important, and have areas that I missed pointed out to me.
A second factor that helped was only reading and working when I was alert. When I wasn't paying attention, I just didn't work. I already knew that was a waste of my time. By senior year, I would work hard for a few weeks, then slack for a few weeks.
I treat the soft sciences and the humanities as vocabulary tests. I'll go through finding all the black words and write them down. The next day, I need to know what each word means off the top of my head. I'll go back and read up on the words that I don't remember. Once I took up that method, humanities became a cakewalk for me.
Writing was tough for me. I write fairly well now, but back then my thoughts were just a bit bucket of bolts tossed across the floor. I could not write a clear sentence, let alone a clear paragraph. My first "F" in college came from my first English paper. I deserved it, too. That F kicked my ass in gear. (It's my personal opinion that everyone needs a few good F's in college. It's good for you.) I decided to learn to write, and I did. By senior year, I could whip out a paper and get an A without much of a huff. I wrote an incomprehensible draft, then wrote the whole thing again, this time ensuring that I actually made sense.
I wiped out on Chem and Calculus in college. They both earned me F's, then I switched to English Literature and was much happier. I think that I could do both those now, mostly because I learned that I have mild discalculia. That is, I swap numbers and signs around in my head. Now that I know about this, I can check myself. Back then, I just didn't know. That, and number stuff just drifts in a little slow for me. When I get it, I really get it. However, getting it can be a trick.
Math and Sciences are also far more sensitive to HOW they are taught. I now know that calculus was just taught to me wrong. There was just a high expectation of me going in a grinding away until I got it. That doesn't work for me. I did the formulas and really learned nothing. I haven't fully worked out math yet. I may just need to take an iterative approach by taking a course, then taking it again, so some variations thereof.
Some things still make my brain spin like nobody's business. That's always tough to get through. It was always this cognitive wall to me. Now I know that I just have to be patient a bit and let the spin wind down. Things eventually become more comprehensible. I can usually occupy myself by using the "learn one thing" principle, which helps me to make little bits of progress until my brain slows down.