This is a link to a great PbP guide:
Building a Better Doomed Hero: Painlord's Advanced Play-by-Post Play
I would like to encourage everyone to use the following posting conventions (source: Generic Dungeon Master)
1. Use ”Bold” with quotation marks for things your character says. ”Wait, everyone, I think I heard something!” I say as I back up against the wall.
2. Use bold italics for things your character thinks. This is supposed to be the building where Martine told us we would find those books, after all, isn’t it I think to myself as my heart begins to pound in my chest.
3. Use italics for questions or comments made by you as a player. Am I still suffering from a ringing in the ears from the explosion in the last encounter? If so, subtract 2 from that roll
4. Use out of character to describe actions your character is going to take, when you want to be clear about those actions (otherwise, it is acceptable to type your description of what your character is doing in regular type. I take a standard action to move as close to the building as I can, from the street, and stand with my back to the wall, then listen carefully
5. When rolling dice, please identify the nature of the roll ["dice=Perception Check, listening:]1d20+3[/dice"]