You can also write your general nuggets of Puzzlebox philosophy here. Here's one that I sent to an applicant:
Here's something you might want to keep in mind as you're thinking about this: Nothing about anyone's life on PB is an accident; in almost every case, everyone is who and what they are because they want to be that way. Everyone has the opportunity to live in almost any kind of society they want and to inhabit any kind of body they want. Figure out what decisions your character and your faction, if any, made and why they made them, what goals or beliefs led them to those choices. Think big and aim high.
It's often said that without scarcity there is no struggle. This is blatantly untrue. The pampered immortals of postscarcity society are still faced with the aggravating task of getting along with people whose worldviews disagree wildly with theirs. Now you can't even kill them all to make them shut up. They'll just be back tomorrow morning and you'll have hardened all their prejudices, making them even more a pain to deal with. No wonder some sentients choose to withdraw into closed enclaves... but those tend to fission within a few centuries, if not sooner.