Give each player a background info on his character, tell him the NPCs he knows and who could appear during the game, stuff like that. I like to give players a text that describes the campaign world beforehand.
The last campaign I ran, the PCs all came from the same valley and belonged to the same clan (something like a Highlander Scottish clan). Then I told them the last clan's leader was dying and representatives of various families of the clan were sent to deliberate, choose a new leader, etc. The PCs were all representatives of family sent to the council meeting. Of course, there was a player playing a gnome, a race that I don't like and was unrelated (should not have allowed gonmes in the first place) to the clan, so I had to invent a stupid excuse for his presence. Anyway, this introduction was fine and replaced the traditional tavern's first meeting fairly well.