GreetingsI do a lot of marking in my books. I have a method that works well for me and involves several colors of hi lighters. ex. In the NEC, I will use one color to hi light each code section dealing with a specific topic like 230.66, 230.70, 230.71 and so on. Currently in my book I used a light green for those sections throughout the entire book. That way when I'm looking for a specific section, I know I'm looking for green. Green will not be used for anything else in the entire book. I break down a book in that fashion so that the colors will jump out. Another thing I do is put a circle in red pen around each number in the entire book. Ex. red ink around all measurements, amperage ratings, numbers indicating amounts like the "two to six" disconnects. I have found that usually about 35% of the questions are dealing with a number. So if I'm scanning a page looking for say a wire size, then I don't have to read the whole friggin page. Just scan the page for the red circles and it really helps. There might be a page or 2 that have a bunch of numerical values so sometime I might just put a red circle at the top of the page or next to a paragraph that has a lot of numbers like 240.6 of the NEC.
In other words I figure up a plan to mark the book so that I have to do a minimal amount of reading. And do the whole book in a consistent manner. Also, spending all of that time marking up the book helps in memorizing a lot of the stuff anyway. Just plan ahead and don't overmark the book. You can shoot yourself in the foot that way.
Tab the books too. I buy the tabs for the book and then I usually throw in a few homemade tabs to stand out for certain sections that I know will come up.
Hope this might help.
BSSTG