One thing editors look for are changes in the growth of your character. I typically concentrate on story, so sometimes I have to go back as I edit a finished manuscript and decide on the area for growth, then follow it through.
My recent historical MG book had lots of action, interesting main and secondary characters, but static growth for the protagonist. So I gave her some fear for what she was about to undertake, at the beginning of the story, and showed how she overcame several fears and became a stronger, more positive person.
A short story doesn’t have that much room for character development but should still show growth through facing conflict. Of course, growth won’t always be steady, but show some slips and stumbles. Isn’t that more true to life, anyway?
So grow those characters and make them more interesting to readers, including the editors!