I know I'm gonna lose some people here but I usually consume books as audio books. It started when I decided I needed to be "more well read" and I started listening to books on my daily commute. I have found that my comprehension and retention of audio books far exceeds when I read a book. I know that for many people it is the inverse. That said, there are certainly books that do not work as audio and some that are better for me as audio.

In my experience most books have a LOT of fluff. Actually, most books suck. I have started and never finished many books for this reason. My perspective is that there is a tradeoff of time and attention with reading a book. I try to glean the valuable info from books. The main idea. When a book is very information dense I may re-read it. There are a few I have read multiple times but it is a very small number. Some books are just so info dense that I have to slow down

Writing summaries is a great way to internalize the knowledge from a book. I don't have a habit of doing this but I do jot down notes and quotes in a text file. What works for me is talking to people, usually my wife about what I'm reading. This year I have been trying to do a better job of journaling and writing as it is one of the best ways for me to clarify my thinking on a topic.