Cal Newport divulges his technique for researching books.
The key to my system is the pencil mark in the page corner. This allows me later to quickly leaf through a book and immediately identify the small but crucial subset of pages that contain passages that relate to whatever project I happen to be working on.
How I Read When Researching a Book by Cal Newport
Such a simple thing to do and yet I wonder why I haven't read of this before. I often fold down the corner of pages, but simply putting a line in the top of the page I can quickly thumb through a book without having to worry about folded corners of pages unfolding themselves and being missed.