I am full of myself, and jsut so happens that i know what I'm talking about, so here you go.
1. Read the last line of the vignette first
2. Read the answer choices
3. Read the vignette last (highlight, and strikethrough)
1. Read the last line of teh vignette first. Ask yourself, what question am I answering? This is going to put you in the mindset of the answers to follow, and will give you an idea of what you actually need to look for in the vignette. Rather than getting bogged down by all the detail of the question, trying to guess what is important and what isnt, read the question first.
2. Read the answer choices. If you are choosing between 5 types of gram negative rods, getting to "gram negative rods" isn't going to help you. If you are choosing between "GPC, GPR, GNC, GNR" well, thats a very different story. Similar concept to #1, you know what to look for
3. Read the vignette last. Step 1 has no curveballs. They also have a very limited amount of space. If they take the time to say something is POSITIVE, then its important. It will separate one or two answer choices. If they take the time to say something is NEGATIVE, that is going to be your clinch pin. That "pertinent negative" essentially takes one of your answer choices off the list.
Try it out. See if it works. Dont be distracted by obnoxious questions with superfluous detail. Hone your thinking, hone your reading of the question to narrow down what is going to be the essential information for you to answer. Win!