In photography, specially in Documentary/Street Photography, not everything is our technical ability to get a perfectly balanced picture but to be able to catch in our memory cards/film that meaningful moment before it pases away. The essence of the captured image could be whether a sensation, an action of the subjects or something that the viewer will instantly catalog as "shot at the right moment while being at the correct location". While the fathers of documentary photography (e.g. Robert Capa, Cartier-Bresson) have very good examples of this, some of their most famous pictures were allegedly staged, namely "The Fallen Soldier" taken by Robert Capa while he was covering the Spanish Civil War. However, we cannot deny that they started what we consider Documentary/Street nowadays and that their work is of paramount importance in the aforementioned style of photography. Their style has influenced generations of photographers, and the key of their success was to give that feeling of capturing an instant that reminds us that "an image is worth a thousand words".
So, we may ask ourselves, how have they achieved that? In my opinion is just one word. Instinct. This might give you the idea that something primordial as instinct is something that one is born with or not at all, but don't worry, is not so much like that. Some of us are born with innate skills that some other individuals completely lack of and vice-versa. My ability to play football (or soccer, depending where are you coming from) is completely negligible, giving place to bitter jokes and a decrease in the level of respect regarded by the observers of my futile attempts (who would have respect from somebody born in Argentina that is capable of falling off by himself whenever he attempts to do something with the ball?). Jokes apart, the fact that we are given some abilities or skills "by default" when we come to this world does not mean that we cannot improve or train ourselves to get better at.
The good news is that we can definitely get better. How? Start to go without the camera to a very busy place, no matter is a familiar or a brand new one. Observe. Keep observing. Look. Stare. Analyse the moment. Got bored of the same place? Walk around, get lost and keep observing. You are going to realise that you need you camera for some interesting interactions that might be happening around you. Possible subjects with another subjects. Subjects with environment. Subjects with subjects and the environment. Look up for places that you think they would be interesting and something could happen at any moment. Learn to predict behaviours. Search for those little moments that transmit you a feeling. It does not necessary mean that they have to have some implied message inside, but anyway you should look for that kind of situations as well. This is a discipline that requires you to analyse a given society at a given place and time. When you have done all of the above and you have already hated yourself, go back with your camera and start trying to get shots. Do not spray and pray. I repeat, do not use your poor camera as a machine gun shooting everything; be selective. Practice, my friend, makes perfection. After some time, you will realise that you are walking in the street, seeing and photographing moments in an instinctive way. Victory.
You might have noticed that by now, I have not mentioned anything regarding the technical skills to get a successful image, but I emphasised on the technique of observation. Whatever Documentary/Street lacks in the technical side, gives it back on impact to the viewer. It's not a discipline like Architectural Photography or Landscape Photography, where the execution of the technical details (namely ISO, aperture, POV, focal lengths, lightning, etc) plays an extremely important part in the final outcome of the image. On the contrary, if we take a look at the early work, we would realise that because of the inferred effect into us by those photographs, we won't be taking in account the technical side as much as another discipline of photography. Said this, this does not mean that technical ability it is not welcome at all, on the contrary, it is extremely appreciated that you could apply it successfully given the short instants that we have to shoot the trigger, but I wouldn't consider that be part of the essence of the image.
Finally, the equipment is completely up to you. You can use a point and shoot, a DSLR, a medium format, a 50mm focal length, 85mm or 35mm. Use your weapon of choice. Do not have strings attached with the preconception that Documentary/Street has to be the "in your face/wide angle" fashion. That has been done already, so is up to you to give your personal touch to photography and to help this beautiful art to keep evolving.
Observe. Analise. Predict. Shoot!