It varies from RP to RP (and I assume person to person), really. I've done one where there was no CS and the character's personality and backstory was built up in the intro posts. On the other end, I've also seen RPs which require a lot of information about each character (for story reasons).

Overall, in my opinion, you can never go wrong with the basics:

[b]Name:
Age:
Gender (if questionable) and/or species (if fantasy/sci-fi):
Personality:
Background/backstory:[/b]