Source: http://lifehacker.com/get-more-out-of-th...

Popova explains how she takes notes on books:

• As she reads, she creates an index at the front of the book that lists its most interesting ideas.
• Every time she encounters a passage relevant to one of these ideas she adds the page to the relevant line in the index. If its a new idea, she creates a new line for it.
• As she reads more, the index grows.

Here's what's great about this idea index method: When you pick up a book read long ago, you can quickly recall what it has to offer by glancing at the index. Then, if you want to grab some quotes about one of these ideas, the index tells you exactly where to look (no more reading every annotation!).