My secret for reading difficult math and physics texts: write out, by hand, every equation as you encounter it. Firstly, it slows me down so I'm not tempted to skim it like a novel. More importantly, my standards for what I write are much higher than my standards for what I read; if I see something I'm not completely convinced of, I may shrug and move on, but I'm not willing to write something down unless I really understand it.