Quick answer for me, as I've often found myself entering campaigns midway, or at least joining established gaming groups, is a "ganger/friend/old coworker" approach. Before entering the game I hash out a quick connection to at least one other player, who then introduces me to the other runners. Maybe not applicable for all situations, especially totally new groups, but it's helped drive some fun RP, even outside of regular runs. Gangs are complex social structures, after all!
