Similar to what others have said, do a quick pass once to get a sense of what the context/main concepts are. pass 2) read the headlines of each section. pass 3) read the bold words of each section and make note of them. pass 4) read the first and last sentence of each paragraph in the chapter. pass 5) read the whole chapter as you normally would. The increased/repeated exposure helps you to contextualize/relieves anxiety associated with unknown terminology/concepts.

Make notes and use "chunking" to group similar ideas into groups and build up from those. It's easier to learn a bunch of small pieces and combine them, than it is to attack an entire subject all at once.

Use multiple sources and YouTube extensively (lectures/enthusiasts explaining difficult concepts). Sometimes a slight tweak to how a topic is presented, along with the context from past passes in other sources is enough to improve understanding.

Work through problem sets and free-recall to avoid cognitive biases of thinking you know some material better than you actually do.

Spaced repetition systems like Anki.

Experiment with all of these (and other approaches) and be objective about which work best for you.

Some helpful resources I've found over the years are:

https://en.wikipedia.org/wiki/How_to_Read_a_Book

https://www.coursera.org/learn/learning-how-to-learn

https://www.khanacademy.org/science/health-and-medicine/exec...