The good ol’ fashioned “You all meet in a tavern, answering a poster offering gold for help…”? The action-scene, “You’re all engaged in mutual mundane task, when suddenly a band of thugs/goblins/whatever bust in looking for the plot coupon and chaos breaks out”? The “Elder Scrolls classic” - all being prisoners thrown in together? Tie it in to a character’s backstory and let them lead the other party members in?
What have you found interesting or successful, and why?
Wouldn’t say that I have a favourite, but one DM I had started the campaign mid-adventure in an old but recently rediscovered ruin. Our characters, who were adventurers, explorers or treasure hunters, just randomly bumped into each other, and after some negotiation decided that there were safety in numbers and joined forces.