Another technique I've used to bring members of the party together moreso than just all being hired for the same gig (for example)... has been to use Session Zero to run the character creation process of Fiasco to connect PCs to each other in the story. For my Curse of Strahd campaign I made up my own playset for it with a number of gothic ideas for relationships, needs, locations, and objects... and then we went through the whole Fiasco process of making connections between the various PCs. Upon completion, t his gave each player two other members of the group that they had a previous relationship with, and also gave them interesting character ideas, concepts and interactions already in mind leading into the first session.