It's very difficult to comprehend

I find researching assignments can be really hard. One reason is that when I'm reading a book, instead of really thinking through the author's point of view, I'm spending about 30% brain power on working out whether or not this particular book is worth reading for the assignment or is a waste of time. Especially for Joyce Meyer books. This means that my actual comprehension of the book is lowered significantly, and thus my speed in finishing the chapter. Ala Mark Driscoll when he hits a hobby horse in his sermons.

Any tips on this sort of thing? Or should my research gathering techniques just be better?