Ryan Holiday, best known for his work as the Director of Marketing for American Apparel and his bestselling book Trust Me, I’m Lying: Confessions of a Media Manipulator, shares his system for doing book research. It’s the same method employed by one of his guiding mentors, the great French writer Montaigne:
Montaigne kept what he called a “common place book” — a book of quotes, sentences, metaphors and miscellany that he could use at a moment’s notice. I keep a more modern — but still analog — version of this book. I write everything down on 4×6 note cards, which I file in boxes. (You could do this digitally, I suppose, but the physical arrangement — being able to lay them out on a desk — is critical to my work).
It doesn’t necessarily have to be a physical book — it could be a text file or a Word document. Holiday handwrites the quotes on several 4″ x 6″ index cards, a system shared to him by bestselling author Robert Greene. Greene describes his method more thoroughly in this Reddit AMA.