How to best approach literature with low information content for good retention
Last-resort, completely-silly trick: When I had to force myself to read through a particularly awful textbook, I decided to read it aloud to myself in a series of silly voices. That actually did make me pay attention to what I was reading, so I could get the emphasis and inflections right... and perhaps surprisingly, I did find and retain the new ideas I was reading for.

Another approach can be to take it as a translation or editing task. Into another language, or into the same language minus the sequipedalian verbiage and jargon. Again, the goal here is to try to make a bit more of a game out of it so it isn't a completely uphill slog.

Note that if you have any interest in publishing your own textbooks at some point, this can be an excellent education in what not to do... you might want to take notes on that too.

Occasionally, the right answer is not to read the textbook at all and just work from the lecture notes. Or see if you can find a set of Condensed Cream Of Textbook notes somewhere -- Cliff Notes-ish things do exist for some books. 

... But in the end, the real answer is "try things and see what works for you."