I recently started taking online classes, which means reading the textbook is no longer “optional” (in quotes because it was always required, even when I didn’t do it). I have a pen and I track the pen along the bottom of each each line. I read to keep up with the pen (although I will re-read if I get distracted and miss stuff). I underline anything I want to remember. This helps because you end up reading the underlined portion an extra time or two, and you have to focus on it as you underline.