I agree with what everyone has said. I found Ob/Gyn and Psych to be the easiest of all the Shelf exams. I used the First-Aid series to study for them though (am not much of a Blueprints fan), but both series do a great job. You should also do questions. Pre-Test and Appleton and Lange are good sources of questions, but I personally liked using Kaplan Q-Book for Step 2. You can buy it at any medical bookstore, and it is arranged into tests by subject matter (ex. Peds test#1, Peds test #2, ob/Gyn #1, etc). I found that Q-book is the most similar to the actual style of questions that you will see on the Shelf. About half of the Pre-Test questions are way too short, and Appleton and Lange tends to be very picky in certain areas that aren't stressed on the Shelf. When you take the test, you need to always be aware of time. Don't spend too much time on one question. I always tried to make sure that I was through question 60 by the time the half-way mark hit, because you start to get test fatigue and tend to go slower at the end. Also, the last 10-15 questions tend to be really long, and the # of answer choices can go as far as A-R (that's the longest one I remember, there may have been some with even more answer choices.
