ORGANISATION
A useful note starts small.
A note is easier to revisit when it answers three questions: what is this about, where did it come from, and why did it matter at the time?
Give it a descriptive title. Keep the source alongside it. Add one sentence in your own words explaining the idea you want to remember. That small amount of context often helps more than saving a long extract without explanation.
Separate a quotation from your interpretation, and mark anything you still need to check. When returning to the subject, the distinction makes it easier to continue where you left off.