I recall a Open University lecture on the radio which contained the suggestion "what was the author trying to distract your attention from?"
You could reread any non-fiction with that in mind or indeed after reading some reviews.
For example in Lois McMaster Bujold's Miles Vorkosigan books there are all sorts of references and foreshadowing that you might only spot on a re-read.
They can be enjoyed even without noticing and enjoyed again later.
visit
http://dendarii.com/accc.html for A Reader's Companion to A Civil Campaign (PDF or ePub)