I set my camera up on a tripod and framed a sidewalk with some windows and a bicycle in old Heidelberg, Germany, waiting for pedestrians to come by. It was afternoon, but still quite bright. I dialed the ISO all the way down (to ISO 50) and stopped the lens all the way down to its smallest opening (f/25). This yielded a shutter speed (shutter speed is not really a speed, and is more coherently described as “the duration of time the shutter is open” ) of 1/5 of a second. The idea was to make the exposure as long as possible to display the motion of any humans that entered the frame as a blur.
With this kind of photography, you have to take many shots to get a good one. Fortunately, a pretty girl in a blue dress came along without too much delay, and did a nicely positioned twirl in my frame, leading to an elegant motion blur.