How many of you annotate books for fun? Im thinking of starting but don’t know where to begin,any advice.

I use them for my favorite parts, favorite quotes, and things that make me feel emotional. Lol
I normally use one color unless I run out of that color.
Some people use different colors for different meanings to them. Like pink for a romantic part or whatever.
Unfortunately I haven’t got the guts to actually write in my books.