Missions, not so much.
We make characters as a group. I briefly talk about the setting and neat stuff going on there, then ask the players to each come up with a notable ally and a notable enemy for his or her character. Those characters invented by the players become the campaign's major NPCs. (Many more are introduced during the course of the game, of course, and characters that turn out to be not so interesting fall by the wayside, but the starting cast is a great launch point.) The tensions between those characters and the PCs become the campaign's major sources of conflict. Mission never really enters into it.
