I read Board Stiff Two, Board Stiff Three (not just an update of Board Stiff Two!), most of Yao and Artusio, and did several mock orals with a retired examiner. Started Big Red but Jensen's writing style didn't really agree with me, so I mainly used it to make flash cards for 40 or 50 of the most common things that I might get asked - not because I didn't know how to handle the situations but because I wanted to be sure I didn't forget to say something that I'd otherwise simply do by instinct.
The five most important things I remember being told were:
1. Almost every answer should have a "because." What are you having for lunch? A salad, *because* salads are nutritious and taste good. Etc.
2. Within reason, it's more important to be able to defend your answer than to have your answer match the examiner's own philosophy. These are board questions for a reason, as Board Stiff Two points out - they're supposed to test your ability to reason through a position on gray areas.
3. Go system-by-system. If you're debugging a machine problem, go from the wall to the patient. Be systematic. If the examiner tells you the pt is now hypotensive, don't say "Hmm, it could be an MI, or it could be dehydration, or it could be anaphylaxis, or it could be..."
4. "Assume" the best possible situation - the examiners will correct you if they want it to be otherwise. How would you get home today? "Assuming that the car is functioning properly and that traffic is flowing normally, I would..."
5. While you have to try to work through the question, you're allowed to comment that you would send this case to a specialist in real life. I got a pedi heart on my boards and certainly used that comment there.
And one thing that worried me, although thankfully I passed on the first try: you may get bizarre, where-did-that-one-come-from questions towards the end of the session. According to an examiner I asked later, it means they went through their questions more quickly than they thought they would and are now ad-libbing stuff to see what you'll say.
Good luck!