There are only a few general ways to get the party together:
the linked background
(each character has to have one of the others involved in the background)
the same place same time
(tavern, market riot, jail cell)
the mutual employer
the rolling stone gains momentum (we start with one, and then add another and another and another as the action progresses.)
Met because a task presented itself
preplanned
(the players sit down and discuss how things happened) (this overlaps with the linked background.)
My favorite however is "in media res": The characters start in an action scene. This is tricky to do, but you build the background as whatever is happening unfolds. "Thorok, you are fighting an orc from the tribe that killed your family as a fireball flashes off to your right" "Mulseen, you were able to see that Morkoth your arch enemy was casting fireball and duck behind some cover ... etc etc. Thisone is hard to get characters to go along with.
Aaron.