To be honest, no matter how creative I've been or experienced from other DMs, the party always meets in some convenient location.
For example: the local RSPCA run by the kindly Monk patron, the service station en-route to a holiday destination, etc.
No matter how convoluted we make the ties between characters pre-game they will always meet up somewhere.
I once ran a game where all the adventurers were 1st level and they had grown up together in a small village and that village was attacked by kobolds and they went off to save their village. Sound different? Not really ... instead of an inn they all met in a village.
Another campaign had me write a complete script for a "movie intro" to the game. Every player had parts to play and read them at the table. It explained each character background, how they got to where they were and why they were visiting the city and more specifically the RSPCA location. But they still met in the RSPCA.
No matter how clever the players are and how they work out their reasons for working together, there still has to be that starting place where they will conveniently gather as a whole to start their adventure off.
That's what I think anyway.
D