If they're a listening audience, telling them part of the story can get them into ballads (I've also nicked Spiers and Boden's idea of casting the movie....) or giving some history behind the song or the times it comes from. Intros need to be snappy and witty and the songs should probably be faster than in a folk club.

If they're not really listening, I wander off into country, rock'n'roll and classic (aka nauseating) stuff like the Wild Rover. Danny Boy doesn't fit my limited vocal range in any key, thanks.