I sit down with the players at Session 0 before anyone has rolled a character and set out the plotline and setting of the campaign, as well as major factions. Then, everyone rolls for who creates their character first. The first person does, based on the info given, and then the next person follows. The only rule I maintain is that all of the characters must be friendly and trusting of each other from the get go. I've had too many campaigns get derailed because someone wanted to be the guttersnipe and not trust anyone else in the party and then it just turns into a slog through trying to convince that one player that it's OK to go along with the plan. Once the characters are rolled, I ask if there is a consensus as to who will be the default leader of the group. If there isn't one, then I have them roll a CHA check, winner is the leader. It doesn't have to stay that way, but it helps to keep the early game organized until players find their footing.

After all of that is taken care of, I'll play through a quick one-shot intro to the campaign to make sure everyone is happy with their characters, then set up the hook for Session 1.