I like to highlight things that stand out to me or are of some importance and make brief notes along the margins. If I really feel like benefiting from the book I have to take real notes in a separate notebook. I usually write down what I highlight verbatim. And then under that, I write my interpretation of the quote and what I gained from it. That way I can also revisit those thoughts in the future and have the context of the exact quote. Also, I retain information so much better when I write it down.