Technical issues aside, photography's about the story you're
trying to tell with the photo. For example:
Does this guy play the violin for fun or to make a buck?

What does this lady make of her photo being taken? Is she
defiant or is she affecting a Mona Lisa look?

What's she so pissed off about?

Is that a boy or a girl in the pram? Twins, maybe?

Girlfriend issues, perhaps?

Or maybe it's just a collection of stories all in one?

Is this a good photo? Damned if I know. What I do
know is that I took it on the fly, and when I uploaded the photo to
my laptop and saw the overall picture, I liked what I had
captured.
The presence of the violinist got me to get my camera out and
take a shot just before I got off the train. Instead of
focussing exclusively on him, though, I decided to take a chance
and take in as much of the scene as my wide-angle setting would
allow, and it turned out to have a pleasing result.
If you're taking shots on the fly, it doesn't hurt to pull the
focus back from what's got your immediate attention. You
never know what else you might get, and you can always crop
later.