When I went and completed my interview with my FFR, before my application was shut-down. I personally just went with the natural, clean-shave to show that I cared, I wore a dress-shirt, with a tie, black dress shoes, and dress pants. I didn't want to go over the top hence no sports-coat, etc, I just wanted to look nice, and show my FFR that I cared about this interview, and that it could mean a lot for my future.
Hence bottom line, just look well-respected, and professional, and everything else should carry itself.
Not to mention, my FFR first mention was literally my clothing, and how nicely dressed I was, so I think that made a good first-impression, before anything else.
P.S. Don't forget a nice-looking haircut, mine before the interview wasn't too long, but I decided to make it really short and just look a bit nice.