One thing I do with my books is I actually meet up with beginners and watch them try to use it. It seems every time I do that I find something new I hadn't anticipated. Like recently I changed the first exercise of LPTHW to have screenshots of what they will literally see:

http://learnpythonthehardway.org/book/ex1.html

I met with a beginner and watched her go through the first exercise, and she didn't understand that she's needed to type "print" and not the line numbers. I talked her through it then realized if I just show a screenshot then people could step from literal thinking about the code blocks in the book to abstract thinking in one exercise.

Same for the terminal/powershell screenshots. People didn't get that they just type into powershell. They thought they had to run python, then type the powershell commands into the python REPL.

Doing this kind of "usability study" on my books, and having the comments on each exercise, has really taught me a lot.