Well, if being the OCS Reg Comm (no big deal
) was any predictor of future success...
In all seriousness, for background I went to OCS as a First Class with 8 years in. Physically, I was already in pretty good shape, being an avid runner. In the two months prior to reporting, I was doing 2 runs a day, with a longer 9-10 mile run once a week. Also was maxing out all the standard PT moves (push-ups, crunches, flutter kicks, mountain climbers, etc). As it turns out, I was way over-prepared physically, but in the grand scheme, that took some stress off of me during the course.
Mentally, my plan going in was to just play the game, roll with the punches and try not to stand out. That more or less worked out for me. I will say, for those who haven't experienced it, that the fear the DIs will induce in you will throw you off balance. That's by design. There's no good way to prepare for the intensity of that experience. Just know it's coming, and that you'll get through it. By the end of OCS, you'll idolize your DIs, but you can't get to that place without going through the psychological transition from fear to respect.
On starting over, during the first week inspection, I was standing there in my Khakis, 6 rows of ribbons, Aircrew Wings and EAWS. Our class officer took one look at me, got right up in my face and said, "You have zero experience at being an officer... Zee Row." That really stuck with me through OCS and well into my first fleet tour. He was absolutely right, and that helped recage the way I looked at things.
I've seen lots of prior officers over the years - some are amazing leaders, others not so much. Those who adopt a "been there done that" attitude usually don't fare well. Far better to use your fleet experience in helping your peers learn the ropes with understated confidence, than to be "that guy" who thinks they know better than everyone else.
Anyhow, there's my $.02
.