Looking at high-quality published work versus aspiring photographer's works, it seems to me that the major difference is composition. Photographs are two-dimensional framed works. Composition isn't a secondary element (after the subject proper) - it is the subject.(posted 8265 days ago)Some good examples of composition (not to mention lighting) can be found in this month's PDN online portfolio of Brian Doben. What's really interesting about them though, is that - even though they are presented as 6x8 aspect ratio and could therefore have been framed in-camera as seen - they had to be shot quite a bit wider to allow for the necessary bleed for print work - and I would argue to get the extremely precise composition that they exhibit.
I have a good eye for composition, but I find that I compose to the viewfinder too much. I need to work on shooting a bit wider to allow for cropping - as well as for different aspect ratios. In particular I'm finding that when I have to mat my wedding shots, I'm encroaching on my subject - and thereby mention making subtle changes to the composition.
As a more practical matter, I'm also finding that people order reprints in more traditional aspect ratios - and that I have many pictures that I can't successfully crop because they were composed to 35mm's aspect ratio.
http://www.pdnonline.com/global/en/professional/features/legendsV5Q3/index2.jhtml