1. Writers complain about the death of short stories, and how there are no markets any more, and no money in them, but I'd like to put this in perspective. Largely, it's just that the markets have changed. There is certainly more emphasis on competitions and anthologies these days, and less on one-off publications in magazines. But everywhere you look, particularly in Wales, there are story collections. They are common in the virtual world. And story writers are hardly alone in receiving small payments. There's even less money for poets, and not much more for most novelists. The lack of material rewards for our writing is a separate issue that affects all artists. As is the fact that achieving publication is tough. The bottom line is: you're much more likely to get your short stories published, than your novels.
2. Short stories are a risk-free zone for the writer to experiment in. They are the place where writers can explore, try out ideas, tackle different subjects, different forms, different voices. Things that wouldn't be sustainable in a novel - purely ideas-based constructs, for instance - are brilliant for stories. You can't imagine a novel which was just a list of emails, or shopping lists - but you could do it in a story. Or your experiments may just be new for you. You can try a male voice when you've always before written in a female one. If your prose is usually unadorned, you can try writing lyrically. Compared with the risks of novel-writing, failure is cheap.
3. You can hold a whole short story in your head in the way that you can't hold a novel. And this gives you the advantage that you can think the whole thing out, give it time to develop, crystallise, optimise, before you commit yourself to the computer. I think many people write their stories too early. Once you have 'expressed' your work, your brain stops developing it. While it remains in your head, with perhaps just jotted-down notes as reminders, it's still dynamic, open to change and improvement. Use your brain like a pressure cooker. Write the story only when you have to, when you've gone as far down the development road as possible.
4. Story writing is fundamentally an imaginative, not an intellectual exercise. If you fail to imagine, you will fail to properly express. Of course the intellect has to kick in later, when you come to edit and hone. To assist the switch, a time gap between writing and rewriting/editing can be very helpful.
5. Don't assume that you have to solve things for your characters. Although all good stories end with a sense of completion, this doesn't mean all ends have to be tied up, for good or ill. There are 'this is how things are' stories, and there are 'this is what happened when' stories. The latter are more likely to come to a definite conclusion than the former, but neither requires you to dot all the i's or cross all the t's.
6. A dozen stories in two years will teach you more about yourself than the novel you could have written. You may actually say as much about yourself in a novel, but you won't recognise it as easily as you will from those stories. This fact about story writing - that you obsess on a limited number of topics, say - isn't always welcome!
7. The most useful editing tool I can recommend is that you READ YOUR WORK ALOUD. If you can't find a human audience, treat the cat. And read from a manuscript, not from the screen.
8. When adjudicating fiction competitions, I have often been struck by how judges' priorities vary, in terms of judging criteria. About the same piece, one might say: 'Brilliant language, very striking and original. But the clanking plot, and the cardboard characters!' The second says: 'Well yes, but do plot and character matter? Surely what's important is that, subtextually, this is a really brave attempt to subvert the Madonna/whore dichotomy.' At which the third sighs and says: 'Well, I don't know what book you were reading, but I thought most of it was incredibly boring, and the rest quite repulsive.'
These differences of opinion occur because there are many dimensions to fiction, whether short or long. There's what happens on the page: the setting, plot and characters. There's the texture of the story: the quality of writing, imagery, accuracy of expression etc. And there's the implicit level, what the story is saying, underneath: the part that demands our participation and offers us, as readers, the chance to be creative too. There are also different dimensions to judges - some rate the imaginative over the intellectual; others vice versa. The best fiction succeeds in both realms.