I believe there is a published dress code for OASC, that said, it is not unknown for the Boarding Officer overseeing the candidates to have to remind them of dress and deportment.
Tip for OASC and as applicable to AFCO: do not have a late night the night before - keep off the Coke, alco pops, caffeine etc. Relax but not so far as to fall off the chair.
Also, new for 2007, NO SMOKING.