The Toughest Part of Dungeon Mastering........well to me at least.

[Warbringer]

Like Celebrim, I have the players chose another player to have a relationship with. Then I tell them the opening context, and have them come up with a reason to be in the context.

Example: in my Ebberon campaign about a decade ago the party was going to the jungles of Xen'Drix.

Elven brother and sister look for the reason behind a strange mark on the sister
Gnome artificer and her malfunctioning warforged friend (T'zitt) looking for the secret to fix him (world view was the secret of the warforged came from the giants)
A pair of Kalashtar seeking the means to overthrow the Inspired - looking for insight in to how the giants drop back the quori
A half elf assassin commissioned to assist ate one of the party (neither me nor the player knew which one)

Act One - Scene One : things turn bad when a Saughin chieftain gets angry at the ships captain for an insulting offer to the shark god for passage. Roll for Initiative

This creates the opportunity for the players to show their stuff, aid one another, even save another players life.

In case people feel this is a railroad, it is a bit, but really the reason for the journey is tied into the player background.

I have 4 or 5 more examples

 

[DragonMan]

For table top games, where the players all know each other and can see each other, I have to contrive some event for them all to come together. If I simply free style it and let everyone get together as they please, then everyone goes off in different directions and I have to run two or more separate groups. In my latest game before they created characters, I told them that they would start together as a group of recruits for the town militia.

However, I used the opposite approach for online games. There no one knows each other and play is reliant on each person's timetable to post on the boards. I started with just one player. As people observed our interchanges, they would PM me to let them join. So I would have the new player be in the same locale as the current players and I let them make their own introductions.