As with art, I know that the best way to do that is to write as much as possible, and to spend time on the craft. No skill grows from a vacuum. The other thing I understand is that clear, unbiased understanding of flaws and weaknesses is key.
So, here's what I need to work on in my short fiction writing: substance. I tend to write little, punchy, emotional vignettes. Characterization seems well-received, and I generally have a solid sense of setting and dialogue and all the nuts and bolts. Sometimes the stories move a larger plot along, but rarely are they self-standing.
I got a story rejection this weekend that said that the piece I submitted felt like a excerpt. This rather solidified my suspicion that this was the case. They liked it enough to ask if there were a longer piece it was a part of that I could submit... but by itself? Not effective.
So. That's my goal with the next bit of writing I do.
In the meantime, have some $%^&* raven feathers: