I'm making a list of things to do for character creation for my first game as DM, and one things I've often heard is to have at least some reason for the players to have come together for their adventures (The traditional ‘we just met at a bar and decided to have some funwe just met at a bar and decided to have some fun’ is a tired cliché...).
What are some better pretexts/explanations on how the characters decided to go on their journeys together. I want the players to be able to write separate back-stories for their characters, but I also want there to be at least a passable story of how they came to meet each other. I plan on them coming from completely different places, so they probably won't be able to have a very long history together, but I still want a decent reason.
How have you explained how your characters met each other and decided to go adventuring? Are there any good guidelines/examples for creating this part of the story? How can I give them a solid feeling of unity for a specific cause, whatever that cause may be?