It's a hard one to answer, it's like trying to describe the difference between a picture and an image. The best way I found initially to dramatically improve mine, was to get in close and I mean real close, a tightly framed subject at the time of taking the image.
The most famous quote of this being by Robert Capa "If your pictures aren't good enough, you aren't close enough".
Also for what it's worth, any element that's in the viewfinder, ask yourself does it add to the final image, if not get rid of it or change the viewpoint, sometimes less really is more.
Hope this helps.