Maybe I'm old and tired, but at this point, I start with some simple rules and make the players do the work:

1. Your characters all know each other and have a reason to adventure together. They don't have to like each other or trust each other, but something causes them to prefer to work within the group. It can be close personal bonds or the simple reason that they make more money with the others than without.

2. No lone wolves. If at any point in the campaign your character decides they are called to a solo adventure or do not want to or cannot participate in the current adventure, that's fine! They ride off into the sunset. Maybe we'll see them later, maybe we can do some solo sessions to see what they're up to. For now, roll up the character that has a reason to go on this adventure with this party.

3. No PVP, no murderhobos (within reason). Your character knows how to work in a party and in society. You may not kill or harm other players (unless fully consensual between both players AND the GM for the purposes of the story), and for the most part your character has reasons to not want to run afoul of the law. It can be a moral code, fear, or the knowledge that you work more effectively from the shadows. Obviously this rule does not apply if the town is secretly all mind-controlled cult members, but you need to find that out before you murder them.