I couldn't think of what better I could have done to improve the
composition in theis image. Any ideas?
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Tough to say without seeing more of the whole scene, but here are my thoughts.
The foreground doesn't do a whole lot for me. In fact, it distracts from what I believe to be the "subject" of your scene (the building and the sky above it). I did a test crop on your photo by chopping off the bottom so that the water takes up the bottom 1/4 of the frame (no grass or sidewalk remain). Already I think it starts to look a little better.
I think that top part sticking out of the building on the right side is a little distracting too, so I'd crop that right edge off.
I'd clone out the crane sticking out the top of the building.
If the opposite shoreline is to represent a "horizon" line, then I think the picture needs to be rotated slightly counter-clockwise... very slightly.
Some of the items off to the left tend to draw my attention away from the subject... such as the dark trees way to the left. I even felt the black windows on the white building had enough darkness to pull my eyes toward them, so I would crop the left side off just to the right of the black windows on the white building. After doing that, I think you have a nice peak that is formed by the right and left edges being lower (and less distracting) than the big building and the awesome sky above it.
The cars are an unfortunate addition to the picture too in my opinion, but you can't necessarily do too much about that.
It's a nice picture, so please don't take my comments the wrong way. I personally would try to frame it a little tighter. I've suggested a lot of crops, which might not leave you with much resolution... so if you could re-shoot this, I would suggest walking right up to the edge of the water, then zooming in a little tighter.
I'm very ameteur, so don't necessarily take my word for it... that's just what I think and see. Try the suggested crops and see if you can see what I mean.