A walk from Westminster to Blackfriars and back, approaching strangers and asking to take their picture.
Being on the shy side, I find this a personal challenge but one which it's critical to address as a photographer. It's difficult enough to control a camera, let alone a mini-shoot, if you're flustered.
And the people I met are lovely. Explain what you're doing and why you're doing it and they're helpful and sometimes intrigued. If they don't want their picture taken, they're polite about it.
Much more chilled than trying to sneak shots from a distance. I can feel a 100 Strangers project coming on.