If you really want to remember the material, take notes. It makes reading go slower, but it's basically the biggest thing you can do to retain non-fiction readings. The other one is discussion, but even when I was doing my socialist book club I made sure to take notes on the readings.

Not only do notes allow you to look back over what you thought about when you read it, taking notes is scientifically proven to help retention even if you never look at them after you write them.

EDIT: Take notes IN the book too. Use the margins, highlight shit, put a sticky tab in there. Future you will thank you.