Also remember that you have the ability to highlight passages (I can't recall if it's highlighting or underlining, but same difference) while you're reading. I was an English major in undergrad, so the following may or may not be helpful to you:
1) Most passages have a general, overall point or argument they're trying to make (the main thesis). The paragraphs or constituent parts of the passage are there to reinforce the main thesis. So basically, you've got the big picture argument, which is being set up by the main ideas in each paragraph. Picking out what those themes are can help you answer 75% of the questions without too much trouble.
2) Context, context, context! If there's something you don't understand (an oddly-worded sentence or an unfamiliar term, for example), look around. Generally, there are context clues to help you figure it out. Sometimes you may not fully grasp the meaning, but you should be able to understand the general theme of the passage.
3) Sometimes it's easier to figure out what the author
isn't saying. Most of the passages on my version of the MCAT would ask something like, "if the author wrote another paragraph, the topic of that paragraph would most likely be..." and so forth. Once you can pick out the themes and the context clues, you should be able to "feel out" where the author could go. There's no algorithm you can follow for this one, as far as I know; but you'll get better with practice.
4) If you don't know the answer, move on. You've probably already heard of the "throwback" questions, and while this doesn't happen in VR very often, you'd be surprised what coming back in 10 minutes will do to your understanding of a passage. The worst thing you can do is sit and stew over the problem.
5) Most imporantly, relax! Easier said than done, I know, but putting yourself under too much pressure might make you miss something that you wouldn't on a casual reading. Use that 10-minute break before the exam to stretch, do some deep breathing, or whatever it is you do to relax. Don't panic and you'll be all right.
Hopefully some of that helps. Good luck!