You should not crop a photo in computer. The idea is that you fill the frame in your camera and keep it like that. For some people this might sound strange, but you will strengthen your eye by knowing how to compose in your viewfinder and not on your computer. After two years of shooting in the street I can compose a shot pretty fast which I will not have to crop at all. This is a skill which really helps you get better. Try it.
For me composition is the only thing to make an interesting photo. Many people think they can make a difference by knowing their camera, making manual settings or knowing all the old masters of photography. The only thing for a good photo is composition. There is so much you can achieve. For me more than 50% of a good photograph is reached with an interesting composition. I wait for direct eye contact. When the person looks to the left, I leave more space on the left. When the person looks to the right, I leave more space on the right. I also like the square format, which is different and therefore interesting. The composition happens in my camera and not on my computer. I prefer to take what comes out of it. If you have to change too much on the computer, you are not good enough.
With lens you can play around with the DOF (depth of field). This helps you to blur the background in a portrait. Although I normally say that the camera is not that important, a good lens with an open aperture can help you making good photos, especially in street portrait genre. You can make an interesting photo from a boring subject, but you can also make a boring photo from an interesting subject. It all depends on our vision and submission of the final result.
When you want to make a difference and taking you off the crowd, you have to choose a different perspective. We as human beings are seeing our life on about 1,70m (depending on your body size). This is a fact. . Everything which we see from this perspective is common and therefore boring, not that interesting. This is reason enough to change your point of view (POV). There are only two ways of changing your POV. You can go either higher (like a bird) or lower (like a frog). Since going higher is more difficult than going lower, I take more shots from the floor. From the floor is very simple and the effect you get is interesting and unique. You can shoot nearly everything from the floor.
When it comes to shooting street portraits, I think the natural thing to do is just shoot vertical (portrait-orientation) images. However try to switch it up. While shooting, try to take both horizontal and vertical photos of your subject. When shooting horizontal photographs, get really close to your subject. It is okay to chop off the top of their head (but try not to chop off their chin). Experiment with different compositions and framings. Sometimes when youre shooting a horizontal photograph, you can just photograph their arms or body language. When you’re shooting vertical photos, try to experiment with uncommon compositions. Put their eyes all the way on the bottom of the frame, or on the top of the frame. Switch things up, and dont just make a typical head-on shot (although this sometimes is the best image). But the take-away is this: if you make a lot of variations of a person (horizontals, verticals, close, far-away), you have more freedom in the editing (selecting) process to choose what you think is the best image. It is always better to have more choices and “optionality”.