I cannot read without a pencil. I highlight the important passages and then I make an effort of memorizing that passages. Think you're a monk and are reading the Bible, reading by verses and memorizing, incorporating that into your knowledge. Take notes of related ideas, expand the text, don't be reductionist, think of the whole.
If I had to choose one recommendation to give others, this would be it. You don't read with your eyes, you read with your pen.
Read fewer (better) books and really internalize them. This 99% of the time requires you to take notes that you revisit throughout and after your read.
