What to do to memorize what you read better
Understand what you want from reading. There's nothing wrong with intending to just learn something out of personal interest. But if you want to memorize it and use it later, it's better to understand in advance how you're going to apply the new information.
Review the main parts of the book. Our brains love new information, but they don't leave out what we do all the time. So a quick look through the book and what's called "pre-reading" will help solidify in your memory the material you're about to tackle.
Take notes. It's best to use marginalia — comments in the margins, through headings, sketches of ideas. This will make you a more active reader and help you remember the information.
Put what you read into practice. One of the best ways to remember what you read is to find ways to use it.
