Now that I can write about my personal experiences without fear of having to take the exam again, I shall dispense my advice freely.
For the USMLE, I used a old edition of First Aid for CS and found it to be sufficient for my purpose. I also looked at NMS review for Step 2 which is quite a good book as well. I fear that I have become a First Aid convert and am proselytizing the world (or at least those that I come in contact with).
I think you need to read all the clinical scenarios and have some idea of the differential diagnosis and investigations you are going to order for each clinical scenario. After that, I suppose you should have a practiced and orderly examination protocol. This is what I did not have, in fact the reason for my first couple of scenarios being terrible was because in my head I did not have any idea of what I was doing. It took me some time to get questions I must not forget and some order to the general physical examination.
In hindsight, primitive medical training more than 5 years old came to my rescue. After a point I was on automatic mode. I was not conscious of what I was doing, it became automatic. I had to keep reminding myself of only the things that I should not forget to do which I had not done routinely as a medical intern, things like allergy history,sexual history and social history. My thought process started happening at the spinal level, never really reaching my cortex. It reminds me of how it was when we were immunising 60 odd subjects in the FGF. After a point, you have no clue as to what you are doing or why - your hands move automatically.
I suppose that was why I was really scared about the exam, because I had not prepared for it well enough and everything I did was reflex. It might have been correct or it might have not. Unlike for my PLAB exam, for which I did a course, spent almost one month practising physical examination scenarios, memorising procedural steps and learning by rote things to say and do in certain scenarios, I did NOTHING for the USMLE exam. I spent less than a total of 10 days studying for about a couple of hours a day reading through the clinical scenarios.
The big difference between the two exams is the marking system. PLAB has consultants sitting at each station who grade you on your physical examination technique, patient interaction and generally pass or fail you. However, the scary bit with the USMLE is that you have these Standardised Patients (actors who have been taught to act or say certain things) who mark you on everything. They have a sheet with questions you should have asked in history,whether the physcial examination was complete and on patient interaction and english speaking ability. This is much more difficult because you need to be able to second guess what exists on that marking sheet of theirs. From what I understand, they have a checklist and tick boxes. Unlike PLAB, where a medical consultant who knows what is important to ask or examine the SP has no medical knowledge. Therefore, you could have asked a very relevant question which does not exist on his checklist and therefore you do not get marks for it. On the other hand, if you don't ask something trivial that does exist on his marking list, you get marked down. The same principle holds true for physical examination. So, I would argue that the PLAB exam is in a way fairer, more valid and more likely to weed out poor physicians as judged by their own superiors.
The other difference exists in the time alloted per station. PLAB has five minutes per station, while USMLE has 10 minute of examination and another 10 minutes to write a patient note. PLAB does not require you to write anything. So the examiner who is a consultant sits in your station and marks you. Its as simple as that. Of course, because of the shorter time limit, you really must be proficient in your examination. Also, the tasks assigned to you in PLAB are far more specific. examples include - perform an examination of the Left knee for this 68 year old woman, counsel the lady about meningococcal vaccination, speak to your consultant on the telephone about a case of abdominal pain that has presented to you in the ER.
USMLE have clinic based scenarios, things you are supposed to handle when you become a first year resident. The idea behind this exam is that you weed out sociopathic or pyschopathic doctors who cannot interact with a patient in a normal way. US physicians and medical schools believe this is the most important exam for any medical student during their entire career.
Most important difference between the two exams - PLAB is only for Foreign medical students, whereas the USMLE is given by every single medic who wishes to practice in the US. Therefore the emphasis as you can understand is very different for the two exams.
Anyway, my last piece of advice for step 2CS - trust yourself as a doctor and you will be fine. As long as you are a normal human being and can hold a conversation in English with another human being you will pass this exam. At least, that seems to be my experience.