Number One Rule of Writing Short Fiction:
Satisfy the reader (i.e. have a complete story).
I knew this rule already, but was reminded again of it by the Underground Book Reviews in their cool series on reviewing short fiction.
Make All Your Words Count
A really well written, short, crisp first chapter uses all the same rules that a good short story will: engage the reader immediately; pull them into your story with action, not backstory; write conflict on every page; make the stakes clear; flesh out your characters and setting to avoid a "blank page" or "talking head" situation; etc. Compelling writing is good writing, whether for short or long fiction. However, unlike the first chapter of your novel, your short story can't just start the story, it has to have rising tension throughout and have a definitive ending. Which brings me to ...
Structure ... It's Here Too
I tend to pants my way through my short stories more than my novels, perhaps because they're a smaller "bite" that I can keep all in my head. But in the end, they still tend to follow a three act structure (granted with less plot twists and subplots and some parts may be implied rather than shown): Act I that sets up the stakes and introduces the characters; Act II where the promise of the premise is played out in a Fun and Games type show; Act III where the drama is heightened, the story question answered, and you bring your reader to an ending that leaves them satisfied. Novellas tend to follow this more closely, shorts (and short-short, or flash) may leave parts out, or have a less character-driven story that explores a concept more than anything. But in the end, you want to make sure you're still telling a story, not sketching a vignette or scene or creating a mood piece (although literary stories may be more stream-of-consciousness/evocative, but that's part of the genre).
Check out Bryan Russel's awesome post on structure in short fiction as well!
Which brings me to ...
End Your Story, Even (Especially) If You're Writing a Prequel or Parallel Story
When I was writing my prequel short story to Open Minds (Mind Games), I knew I couldn't just do a teaser, or a first chapter. Yes, the prequel is great marketing - many people are downloading the free prequel and going on to buy the series - but only because the best marketing for any writer is always the work itself.
As I mentioned before, I found that novellas, with their longer wordcount, allowed more bonding with the character. While I'm writing two more short stories in the Mindjack Universe, I'm also finding that I'm stretching my "short" stories into "novelette" length - i.e. closer to 10k than to 5k. Partly because I feel I need that many words to put the character through their paces, so that the reader bonds with them, and partly because that's just how the story turns out.
Even though these stories are still "short," it occurs occurs to me that they are drawing on a fully developed storyworld, plus the promise of more in the novels. This is all great, but it's insufficient for short storytelling unless there is a beginning-middle-end, an encapsulated work, all to itself. It helps that these stories are from alternate POVs: Mind Games is Raf's story, The Handler is Julian's story, The Scribe will be Sasha's story. While we'll see these characters again in the books, they have a story arc that fits within the short form, because they're plucked from the background of the characters to illustrate their conflicts by showing an event from their past. I'm finding this not only is fun to do, but is helping me more deeply understand my secondary characters (which, not coincidentally, will help in writing the third book in the trilogy).
Stand Alone Shorts
Your short story (obviously) doesn't have to be connected to another work, and I'm looking forward to writing/publishing some stand-alone shorts as well. While short stories clearly connected to your books can "sell" the series, I believe stand alones can do the same thing. This was brought home to me while reading a fantasy romance short story: I found it on the Top 100 FREE list and downloaded it because it looked interesting. I normally don't read fantasy romance, but the sheer power of her ability to render tension on the page and write a compelling story had me seeking out (and buying) two more of her novellas.
That, my friends, is some good storytelling. Again, your writing sells your writing. Getting it into the hands of your readers is the most important step. This is one way shorts (and free) stories can help you market all your other works.
Short Stories vs. Novellas (oh and novels too)
Raised in the (not so distant time) when wordcount was driven by what agents/editors were looking for, these are the expectations I had/have for novel/novella/short stories:
YA and adult novels 80-100k (unless you are G.R.R. Martin)
MG novels 50-60k
Shorter MG novels/Novellas 10-40k
Short stories 5-10k
This was reflected in the books I found on the shelves, as well as the books I wrote:
YA novels (80-100k):
Twilight - 120k
Life, Liberty, and Pursuit - 100k
Hunger Games - 99k
Across the Universe - 98k
Lightning Thief - 87k
Open Minds - 85k
Closed Hearts - 85k
Harry Potter#1 - 77k
White Cat - 76k
MG novels (50-60k):
Hunchback Assignments - 63k
Dark Life - 62k
Clone Runners (not published) - 60k
The Familiars - 58k
Artemis Fowl - 56k
The Faery Swap (not published) - 55k
Shorter MG novels/Novellas (10-40k):
Justin Case - 39k
How to Train Your Dragon - 30k
A Series of Unfortunate Events - 24k
Frindle - 16k
Short Stories (5-10k):
The Handler - 10k
Full Speed Ahead - 8k
Mind Games - 5k
A 100k novel is about 400 pages, so every 10k is about 40 pages.
Only now, I'm seeing a lot of shorter stories on the adult bestseller lists than you will find on the paper shelves:
The Marriage Bargain - 212 pages (53k)
Halfway Home - 203 pages (50k)
Post Human - 182 pages (45k)
Wool - 56 pages (12 k)
Yesterday's Gone: Episode 17 - 68 pages (17k)
(And there are many full length novels, as well as G.R.R. Martin's 819 page tree-killers.)
And some popular serials ranging from novella to full-length novels within the series (these have all sold in the 10's of thousands or more):
Beautiful Demons by Sarra Cannon - a series of 7 (34k - 57k each)
Wool by Hugh Howey - a series of 5 (12k - 63k each)
Ethereal by Addison Moore - a series of 6 (48k - 110k each)
The shelves are no longer governing book lengths - ebooks are erasing the barriers that paper shelves and magazine restrictions used to impose. Whether reader expectations have changed is a different question, but I think we're seeing a rapid change on all levels: writing, publishing, and reading. Interestingly, even at 85k, readers still complain that my stories are too short (in a good way, I think, because they want more):
For readers adapted to full-length novels, are novella's long enough? Are short stories attractive? I think the answer must be "yes" for the right stories, ones the readers love, or they would not be selling as well as they are.
All of this makes me stop and think about why I write the length of story that I do. No longer tied to paper or agent expectations, what should govern the length of a story? I'm averse to the idea of "breaking up" a story just to write/publish installments (see Yesterday's Gone above) - that just wouldn't work well for my writing process. And I'm not keen on the idea that readers won't "wait" six months to a year for a full sized novel - I think they have no problem remembering they loved your first story when the second comes out.
On the other hand, I can see writing an episodic serial, with a series of shorter novels bringing the story out more quickly to readers and creating a different kind of framework than the traditional "trilogy" approach. Or writing a series of short stories sprinkled between novel releases (like I'm doing with the Mindjack Trilogy). Or even writing short stories to explore the world that you're creating for your novel series, before it even debuts (like I'm considering for the series after Mindjack).
In short (ha! like this post is short by any measure), everything is in play - I believe that ebooks have liberated writers not just by allowing them to publish what they want, when they want, but to WRITE free of constraints of any kind, be it genre or length or whatever new thing those crazy creative types can dream up.
The only true rule: deliver something readers love.
Just be careful about giving the readers something new and intriguing - they may demand more, as they did with Hugh Howey's Wool series. Which, in the end, is not a bad problem to have.