How do you annotate a book?

If I can, I find a copy of the book in a second hand store, the mustier the better. Then I don't feel bad for marking it up and making annotations. Kinda like scrapbooking. I don't do this much since hs, but I like how it ends up looking. 

Hi :)

I usually annotate with a huge amount of sticky notes in different colors and each color resembling a different emotion I had while reading said highlighted sentence.

At first glance it always seems like a pretty good and organized idea … if only I wouldn’t forget what color I picked for which emotion all the time xD