Sometimes with fiction books in particular, taking your time to read is important if you want to retain a lot of the information. For example, my house mate can read a novel over breakfast, and retains very little of the story in the long term, while I may take a good 5 days to get through the same book, but I will remember the story almost as if it were a movie, or my own dream. So i guess if you take the time to visualize everything you read, you are processing the information on a deeper level than if you are just skimming through the main ideas of a chapter.
One important thing I have learnt in my studies (psychology), is that you will remember something much more effectively if you self generate the information…maybe after each chapter you read jot down the main events, and the main characters.
And of course if you can relate the story to your own life on an emotional level this helps with retention….read the book as if its happening to you… empathize with the characters. It works, think about most of the movies you remember for years and years, they have something you personally relate to, and are emotionally charged, its the same with books.
Also finding chapter summaries, or discussion forums online after you have read the book helps…thinking about the material in a different way will help memory too.
I don’t know if any of that helps, I feel like I have written down what you probably already know…