I always remember a folkie busker (morris dancer etc also) in NZ. He was an engineer so he had it parameterised pretty well. He chose an underpass/walkway from Wellington Station to the busses - people walking briskly and he only busked on Fri morning commuter time. Last workday people feeling uplifted so he did a lot of jaunty mmorris tunes and would time it to the rhythm of their feet. The wide corridor was echoy so he played at the station end and played to the echo.
Purely as a consumer I notice that:
Sad music needs more work to engage the listener. It helps to smile more than not.
Other than that you have to play what they know or, like Dave, play what their body knows.

I do remember seeing a busker who put a slotted box on the dog and the dog was pretty good a reading peoples intentions, sidling over and looking up dolefully - I think the dog was really the act.