Platypus

Either a large piece of buttered toast or a bowl of yogurt.

Writing notes by hand has been proven to be more effective than typing. Take notes by hand as you go through the source material, then rewrite them (still by hand) into a neat, organized document. Index the document and store it. The act of writing out and engaging with the information to reorganize it will go a long way towards improving recall later, and if you do forget you’ll have a quick reference ready to brush up. Bonus points if you add a section to the neat document linking it conceptually to other knowledge, as that builds even more pathways in your brain to that information.