I recently came across Jordan Peterson's guide on how to write an essay. It included one of the best and most practical guides on notetaking that I've ever read.

According to Peterson, the purpose of taking notes is to understand what you're reading at a deep level and to enter into dialogue with the writer of the text. Highlighting, underlining or copying text word-for-word isn't an effective way to do this. During the act of reading, the reader has to be aware of what catches his attention in the text. Is this an interesting, or important point? Do you strongly disagree with the argument? Has a question popped into your head? If any of these are happening it's a good time to slow down and take some notes. 

Notes shouldn't regurgitate the original text in minute detail, but rather should summarize to eliminate detail and convey only the most important bits. To facilitate this, don't look at the text while you're writing notes. Look away from the text and say out loud, in your own language, what the text was about, then write that down. This takes you out of a passive mode of consumption, and puts you an an active mode of creation, which should make ideas much stickier.