Lesley's post on characterization tools inspired something I've been thinking about a lot, which is Shortcuts to Characterization. This is important in short stories because, well, they're short.
- The Redshirt. Killing off a Redshirt can prove the foe is serious. But please give your Redshirt a name and a real relationship to your protagonist (which admittedly moves them somewhat out of the realm of Redshirtedness). When s/he dies, make it count. This is an opportunity to advance plots and create reversals within your protag, so make your Redshirt work for you.
- Less is More. Keep as few characters as possible in your story, and try to keep only two talking in a scene at once. If you must have more than two present, then give a reason for one or more of them not to talk--busy them with readying the ship for flight, make them an underling (who will perhaps spout off with something surprisingly helpful or do something stupid to raise the stakes), or perhaps an alien who doesn't have their language.
- Show Me The Money. Showing takes far less real estate than telling. Just let your character be who s/he is. No need to explain every action as long as they are true to character.
- Fightclub. Deep conflict brings out your characters' real colors. Experiment with keeping every word they say and every action conflictual and watch your character shine.
- Drop the History Lesson. We don't need to know everything that led up to this point in your protagonist's life. Devise a simple reason rooted in character - key word being simple. Certain people just draw conflict, by way of their career, personality, upbringing, or position in life. And there is a certain elegance in simplicity.