i've just started taking notes and i retain way more
i think its super important to both note down good quotes (for sharing or remembering for later), important key concepts (to help u understand), and then summarizing it how you can, or even summarizing what you don't get, what you feel is missing, what conflicts with other things you know or other authors, etc. But depending on what i'm reading, i'm not gonna critique it or summarize it, just take notes on the basics - other things i feel the need to summarize but there's maybe not enough technical points to write down – do it how you think is best, but write down whats important. That's literally it. Also really get down and cozy with it, make sure you're concentrating.
A friend of mine always has trouble with jargon words and weird complex grammar, so make sure to stop and look stuff up, read smaller materials (you find online) to aid with the main one, and take ur time re-reading when u don't get smth.