Well! It seems to me that the most important parts of crafting an excellent story go in this order*:
Character -> Plot -> Setting/Concept
The order in which I craft stories is this:
Setting/Concept -> Plot -> Character
You may notice a slight problem.
In practice, my backward approach means that the stories I sell are the lucky few that happen to have good characters. What I ought to do is stick with my setting/concept bias, sure, but immediately engage the emergency writing brakes and think about character foremost. Sure, the setting will inform the character. But crafting characters after you've written the plot? Feels a bit like Prometheus to me. The crappy movie, not the helpful Titan.
Without good characters, I think you're really making it hard for yourself to compete with other submissions.
To that end, Chris Andrews has collected a bunch of great responses about the things other writers have learned about creating characters:
I’d tell myself to figure out what my characters want, what they need, and to understand the difference, but that’s just a tiny part of creating characters. Here’s some more fantastic responses to that question.
Read them here, they're quite good: http://fandelyon.com/things-i-wish-i-knew-about-creating-characters-when-i-started-writing/
*This is a high level overview. I realise all these steps are intertwined and sometimes the setting is the character.