Feynman's Learning Technique is effective for learning a new things, deepening your understanding of what you already know.
This technique can be explain by figure bellow.
First step, pick up a topic you want to understand and start study it.
Once you know what it's about, take a piece of paper and write it down as if your teaching someone else. Whenever you get stuck, go back to study and repeat the process until you can explained it from start to end.
After finish this stage, study the topic again. But this time, simplify the explanation use your own language, or use a graphic analogy. This will make you realize which part you already understood and which part you still have a gaps.
If you end up wordy or confusing, you probably have not understood well enough, then you should restart again.
Once you can explain a idea in simple language, you have understand it deeply and will remember it for a long time.