Some of the most interesting photos I enjoy looking at (both mine and other peoples), are those captured in the street without warning or scene composition. Just take the snap! Some images I take don’t appear to be that interesting right now, but look back on them in years to come and you get a glimpse of how people lived in the past. How did they dress, what were their surroundings, what were they doing, what has changed.
You need your camera set to Shutter Priority [S] and a high shutter speed needs to be selected to overcome motion blur and camera shake.
Small is beautiful. The smaller your camera, they less likely you are to having people reacting to you taking a photograph. Big DSLR’s draw attention and make people camera shy. Go for a small good quality compact camera that no one cares about if they see it.
Be candid and stealthy. Once again the small camera wins over the big DSLR. I hold my camera down at waist level, turn off all sounds (beeps etc.) on the camera and hold it in a manner that looks more like I am carrying it rather than using it. My thumb is on the shutter release not my usual trigger finger once again to give the illusion the camera is not in use. And I blast away! Obviously without looking through a viewfinder or rear LCD screen I only have a vague idea what I am snapping, but if you take enough, when you sift through them you should find pure gold.