Study skills advice I disregarded as a young boy:

Underline what is important.
Summarise in your own words.
Space out learning those summaries, longer and longer.

I got stuck on "what's important". And the effort of "my own words".
Now I know this from an article that finally framed it:

Underline what exudes energy.
That energy answers a question you already have. Find that question in you and write that down.
The energy can be satisfied by writing the answer to your question in your own words.

And that last step is deeply satisfying to me.