Pace is not something I am particularly reasonable about when it comes to reading. Rather than savoring a book, I get too excited and tear through it. While there are worse habits than voracious reading, it became increasingly difficult, if not impossible, for me to recall any information prior to the most recent books I had read. But over the past year, I've developed a reading and note-taking system to help me reference and retain the best mental models and insights from everything I read.
The motivation behind this system came from actively seeking a more effective approach to reading. I wanted to transition from hammering through as many new books as possible, to rereading and better understanding the principles and ideas in the most important books I already owned.
Rather than reading a book from cover to cover, then placing it back on the shelf, this system has three steps:
1) Actively engage in the book you're reading, underlining and note taking (in the book) as you go.
If you consider this destroying a book, you would be horrified to see how most of my books look. This helps me focus on what I'm reading and avoid an autopilot state where I black out for multiple pages, unable to recall a single word.
2) Once you've finished reading, set the book aside for three weeks on a separate "to-be revisited" shelf.
Let it marinate. Why three weeks? At this point the book should be teetering on the edge of your short-term memory, distant enough that you can barely recall it. More on this later.
3) Pick the book back up and type out your most important underlines/notes.
Consciously revisiting the content of a book and documenting its most valuable passages is one of the best learning methods I've found. I use Evernote to catalog and record all my notes so I can easily reference them at a later date. Short term, this is not the most efficient process in the world. But it's the most important step for me and saves significant time in the long run.
This system bridges multiple learning disciplines I've used in the past. Steps 1 and 3 were practices I developed as an undergraduate. Rather than studying in the traditional sense, I would underline important sections of required readings and take detailed notes in class. When it came time to study for an exam, there was nothing new to learn. I had already actively engaged in the content. I would simply retype my notes and the important underlined sections, to help jog my memory.
Step 2 was a trick I picked up when I started learning Mandarin. Rather than taking a traditional approach to language learning, I used the tactics outlined by Gabriel Wyner in his book Fluent Forever. Wyner emphasizes a few key steps to learning a new language: learn pronunciation first, don't translate, and use spaced repetition systems (SRSs). The SRS method gave me the initial idea to establish a three-week buffer between finishing a book and revisiting it to type out my notes.
The idea behind spaced repetition is that if you can consistently test yourself right before you forget certain information, you can double your effectiveness in recalling it. I used Anki (think digital flashcards) to test myself in Mandarin. With each time I was able to successfully recall a certain sound/word/character, the time before reviewing that same flashcard grew at increasing intervals (three days, one week, three weeks, etc.).
Of course, learning a new language isn't identical to retaining what you've read in books. The constant repetition is absent. But there are various disciplines and practices found in seemingly unrelated learning experiences that can be effective when applied more broadly. Readapting the concept behind spaced repetition, as well as my reading/note-taking system from college, are examples of just that.
The goal of this system is not to memorize passages like you would foreign vocabulary. The goal is to commit the most important themes, mental models, and insights to memory, so you're able to more easily recall and leverage them in your own life.
But the most important part of this entire process, for me, is the act of actually typing (or writing) my notes back out, and avoiding the convenience of copy and paste. It forces me to consciously revisit the information I've read. And unless you have a photographic memory, you're going to have to put in some work in if you wish to better retain what you read. For an example of how these look, you can check out my catalog of book notes.
I use Evernote to capture all my book notes, which are catalogued in their own notebook. I would recommend a similar service or system so you can easily search your notes and revisit certain sections. Rather than digging back through a book looking for a single underlined passage that I vaguely remember, I can do a quick CTRL + F search and find what I'm looking for in a matter of seconds.
The benefits of this system are threefold: it helps me stay immersed in what I'm reading, better retain key information, and it's searchable. It's not about memorization. It's about arming yourself with the best mental models and insights uncovered in your readings, which you can then apply to better yourself and your understanding of life.
Again, this is the system that works best for me. There are dozens of approaches out there. Research a few and tweak them to your own learning style. Don't be afraid to combine different methods and create a system of your own.
 Wyner, Gabriel. Fluent Forever: How to Learn Any Language Fast and Never Forget It. Pages 40-41. 2014.