A quiet place for things worth remembering.
A useful note captures an idea in your own words, along with the question that led to it. A short example often makes the idea easier to return to than a long list of definitions.
Leave room for corrections. Understanding changes as you revisit a topic, and the earlier version can be a helpful record of what you learned.
A few pages read with attention can be enough for one day. After reading, close the book and write down the part that stayed with you. That pause makes it easier to connect a new idea to something you already know.
Start with one clear question and a version you can finish. Keep a record of what worked, what surprised you, and what you would try next. A finished experiment is a good starting point for the next one.