'Non-fiction' is a pretty big category. What type of stuff are you reading?
Right now I'm reading "The Black Swan." Next, I plan to read "Surfaces and Essences." So I would say popular science recently.
I know textbooks are designed to do the work of drawing out main ideas, explicitly define main ideas, etc., but I would still be interested in learning how people approach textbooks.
I've already read about how to read scientific papers, which seemed like a great resource: http://violentmetaphors.com/2013/08/25/how-to-read-and-understand-a-scientific-paper-2/
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.