I am doing a writing course and the teacher mentioned annotating books to see how the writer writes the book etc. I love books and I hate the thought of a single bend in the book let alone writing in them! However it does seem like a good idea and I'd like to know how you annotate and what do you annotate to give me ideas and a good start.
I don't really annotate very often, if at all. If I come across a spot that sticks out to me and I want to remember it, I'll underline it in pencil and put an asterisk next to it. I've only used pen a few times. That said, I absolutely marked up my college literature books. Looking through them it's a mix of things that stuck out to me and things I thought my instructors wanted me to see.
I buy spiral notebooks at the dollar store and when I am reading a book I always take notes and add to that whatever thoughts I may have about it.
Stick record/index cards between the pages and write on those. Make sure to also jot the page no down on the top in case the cards fall out or you want to take them out (for example when lending the book to a friend without them seeing your cringe-worthy notes about how moving you found the platitudinous passage on line twelve). Does make the book about 50% thicker if you write a lot of notes. Buy thin cards.