For cerebral learning (as opposed to something physical):

Keep a notepad or computer handy while reading, listening to podcasts/audiobooks, and watching videos.

Make notes on everything - basic framing, details, things you’d normally memorize, etc. Draw connections between what you’re learning and other things you’ve learned. Try to identify patterns.

Also try to dig into the source material for the material you’re studying - ie: bibliography, foot notes, inspiration, etc.

Then a day or two later, try to write about those concepts in your own words.