I’m not sure about ‘most inventive’, but I love footnotes in fiction texts. This started with reading the Bartimaeus Trilogy as a kid, as the titular character uses them to add in their commentary to events. Later I read Terry Prachett, which likely inspired Johnathan Stroud. Neal Stephenson uses them well, too, in my opinion, for the Baroque Cycle, and Anathem.
I used to go up to my grandparent’s cottage each summer, which had no electricity so the primary leisure activities were swimming in the lake, going for a canoe ride, and reading. I remember reading The Lord of the Rings trilogy during a rainy period in about a week.
I find I tend to read a lot just through routine these days, I read for about 30 minutes to an hour before bed each night, and then for most of the afternoon on Sundays. That works out to about eight hours of reading a week, and most novels take me about ten hours, so if I get on a series I can generally get through them quite quickly. Usually I like to pace myself on series, however, so I’ll read one book from one series, then read something else by another author, and then go back to that series.
Best way to get better at anything is to simply do it more. If you’re finding it really difficult to improve, it may be that you have some underlying issue (like dyslexia) impacting your ability to read, but there are strategies to get around that.
As for studying, I recommend preparing your own flashcards–that exercise itself builds some understanding because you have to break down the concepts–and use them to help with things that you need to memorize. I always found writing things out from textbooks way more productive than just reading and re-reading the same passages over and over again. There’s some learning science behind that, about how you’re forced to engage more of your attention and process the information more thoroughly when writing it out than by simply reading it.
If I’m going through a particularly hard time, I’ll put an emotionally difficult book down and read something else. Reading is my leisure activity, a way to relax, and an escape, there’s no sense in making it an emotional slog. Of course, when I’m in a better headspace, I’ll pick it back up, because often the emotionally punchy works are the most rewarding to read.