There is a procedure I follow taking a documentary image.
First, get a shot, any shot, without regard to framing, correct exposure or careful focus. This becomes your back-up image. In life things can change incredible quickly and if not for your immediate shot, you might lose it all.
Then carefully improve the first image, with careful selective focus and exposure. I then go on to careful framing to exclude the unnecessary and dramatize my original concept. Along the way, if I'm working with people, I get their eye, so they see my attention to them. This puts them at ease and allows me to continue. There are exceptions to this rule, depending on your personal safety and the risk to your subject as well.
Many the times I have also instructed the subject to disregard me so they don't take away the very reason I stopped for the photo. I tell them, what you're doing is just perfect, don't help me with any changes.
Of course this doesn't always work, but I feel it still is necessary to say. If I had communicated with them, I now owe them a copy of the image, for their co-operation, so this is the time to find how to deliver. In the internet age, an email is usually enough and they will often give me permission to exhibit them.
One of the exceptions to documentary images, are friends or could be friends doing illegal, not necessarily immoral, actions. No photos of one smoking pot or carrying on in some sexual manner, unless there are conditions both of us to agree to. Exceptions to this rule can be civil unrest or true criminal actions, where your image will help the general good of society.
An interesting note ...The closer you get to your subject, the more they will ignore you, as a defense mechanism. Once you are noticed, shooting within 5 feet is easier for both of you than if you are still 25 feet away. Try this out and get back to me with your results.
My photograph of the swallowtail butterfly was my first shot, as my improvements didn't work out, but I still had my back up image, which I then magnified.