Find the stranger's sweet spot.
The Brazen Careerist uses a journalist as a model conversationalist. This isn't a good idea because she has a professional format to guide her interactions with strangers and you don't.
Here is her key recommendation: Ask questions until you find a topic the stranger knows something about. Then let him gab.
Socially savvy people learn the standard form a conversation with a stranger usually takes and practice ways to navigate it. But many of these experienced speakers are not artists and their conversations are hackneyed and sound canned.