There are street photographers who are like ghosts. You don’t notice them and you certainly don’t notice them photographing you. They carry small cameras and they have learned the trick of focusing the lens by judging the distance between the subject and the camera and adjusting the focus ring based on that distance. Basically, they shoot from the hip, with wide lenses to compensate for framing defects as they don’t actually see the frame, they can only guess it. With such a behavior, it is normal not to see them. They are not paparazzi, but the people tend to control themselves when a person aims a camera at them. By shooting without their knowledge, you can capture genuine expressions which are the heart of street photography.
Stalk people. It’s not illegal on the street. See a person you like, walk with them, follow them until you can get a shot of them. Go for public places so you won’t get the police on your head. Try to follow facial expressions and move like lightning when one that you like comes up. It’s all in the expression, and that’s what you’re supposed to be hunting. Never take close shots. Make the subject and the surroundings a part of your composition. Some bland in, some stand out, but that’s the diversity and the fun of it. A suit and tie in an abandoned factory looks better than a homeless in an abandoned factory. Contrast is the key.
Carry small equipment. Do not go street photographing with big heavy cameras and lenses that look like bazookas, people will notice you right away. Use small cameras, the smallest possible, because quality is not an issue. the best street photography in the world has some of the worst image quality as well.
Always ask for permission afterward. Take your shots, then talk to your subjects. It is extremely unfair and annoying to them to find out they were photographed later on, when your work becomes public. Respect them and, if required, respect their privacy.