You can read something and hope that it will all be beamed into your brain for future application. Or you can read it and write down what you just learned, as if you were teaching someone else, and actually retain it. This is called the Feynman Technique.
In other words, implement a more "active" way of learning, which obviously takes a lot more work than it sounds. Ideally, when you write down your learnings, you'd also repeat what you wrote aloud, like a teacher instructing a class. With this method, you discover all the areas that need improvement and can go back to focus on those weak points. Repeat this until you can explain the topic or idea in full and simple details. "Once you can explain an idea in simple language, you have deeply understood it, and will remember it for a long time," the video explains.
We're aware this isn't earth-shatteringly novel or exactly news, but it's simply a good reminder that you are truly knowledgeable about a subject when you can teach something to someone else and have them understand it.
The Feynman Technique [Sprouts]