According to this story in Vox, you have to do something with the information like making flashcards, or diagramming the information.
Aksing yourself questions is also important. "Say you're learning about world history, and how ancient Rome and Greece were trading partners. Stop and ask yourself why they became trading partners. Why did they become shipbuilders, and learn to navigate the seas?"
Researchers also say that spacing out your review helps more than cramming.