[quote=Kaga]
Instead of a strict posting order, you should just encourage players to wait for everyone else their character is interacting with before posting themselves. If you're in a group with three other characters, then wait for those three before moving on, as opposed to just jumping in again after only just one.
[/quote]

This is my preferred system, but it depends on everyone respecting the others they're interacting with. If one rude person steps out of order, without consulting others or giving them a reasonable time period in which to post, the whole system collapses. That's not really fun.