Write as you read. Write on margin of the reading material if you do not plan to resell it. Re-writing what you just read makes you think and it reinforces the ideas themselves. Ask yourself "Why is this information important?" before jotting down the notes. Get inside the writer's head and think about his or her motives in making the arguments that caught your attention.
Draw as you read. A simple diagram connecting the main ideas in the previous and the current chapter helps you formulate the broader picture and retain the gist of the writer's thoughts.
Highlight important text using a highlighter, or a colored pencil. Do not highlight everything that appears important at the first glance. Take care to pause, and reflect, before you highlight.
Underline the important passages with a pen or pencil. If you are underlining too much, think before you lift the pen. Ask yourself -- "is this important information?"
Use yellow Stickies to record your thought and post them on the edge of the page or over the sentence or passage you want to remember. Stickies act both as a bookmark as well as a reminder.
Keep a reading journal and write notes while you are reading, when the ideas are still fresh in your head. You may want to add notes after each chapter or after you finish the book. Type the notes on a computer and save them for future reference.
Make three columns on an Excel sheet and summarize the book chapter by chapter as you read each one. Print the sheet and stick it in front of the book as a quick reference for the content of the book.
Post your thoughts as your Facebook "status" if you want to share them with your social circle. The feedback you receive on "status" messages help you internalize the thought so that you can remember it for a longer time. You might also want to "tweet" an idea you discover, using Twitter.
Make note-taking a habit so that you automatically pick up a pencil when you pick up a book.