When the director of an international short film festival suggested that short films were wonderful stepping stones to features, many film-makers boycotted the festival. They consider short films to be an art form in and of itself. Not as a calling card, not as a training/learning opportunity but something that has been for too long devalued and ignored in favour of the feature-length film.
In the real world however they are used as a calling card and whether it becomes a large budget film that wins festivals or a doss with a digicam, you will learn from the process and the end result will attract attention if it's good enough. I do think it's useful having a short or two in your portfolio but you don't have to if you don't want to. Some writers say if you want to write features then just write features.
Technically a short film is one that's less than 40 minutes but the reality is the shorter the short the easier it is to programme at cinemas or on television. Something between 5-15 minutes is the usual but I would strongly suggest that you avoid going over ten minutes. If you need longer to tell your story then choose a different story.
I think the crucial thing to bear in mind is that a short may require as much planning as a much longer film. It means less time writing out the script, obviously, but the vast majority of the time spent writing a screenplay is spent on laying the foundation work. Working out what to leave out can be more difficult than working out what to put in.
Story
Of course your short, like any dramatic writing, doesn't have to tell a story at all. It could be experimental or arty. However the market for short films is quite small and competitive in the UK and producers are generally looking for writers who can tell stories because distributors want quality stories.
Quality stories that appeal to producers doesn't necessarily mean lowest common denominator stuff, it's also an opportunity to tackle serious issues.
This story doesn't necessarily have to be a traditional three-act one with a beginning, middle and end (although that is what the audience is most familiar with) It could be based on a single event or a character portrayal. But it's got to be interesting.
I think, as always, if you start with a good character then you can't go far wrong. Audiences are unlikely to watch characters they don't care about whether they are in a feature film or a short. Once you've spent time creating the main character then give them a clear goal to achieve or problem to overcome. Another point is that while it helps for the main character in a feature to be likeable, the audience will be prepared to follow a dislikeable main character as it's only a short - as long as they are interesting,
Some people try and cut their feature film down to size or use a scene from their feature film for their short but that's silly. I'm not stopping you (although I do have the power to do so) but a short film should work independently which means a simple idea and story. Equally if you have a two-minute idea it isn't going to work as a ten minute film no matter how much you pad it out.
Technically, with the advance of digital video, making your own film is easy. In fact it's possible to write, film and edit a film over a weekend. However getting anyone to show it, much less buy it, would be a problem.
There's no substitute for spending sufficient time planning and writing your short.
Kim Leggat, Short Film Bureau: “With short films, writers must get to the meat of the story quickly and cut out all the fat. That means broadstrokes. Shorts move faster than features and flaws stick out like sore thumbs, so the stories must be as polished as possible. That is why very few short films work. To a large extent, shorts must be more polished than features as there is so little time to get the whole story across.”
Dick Ross, National Film and Television School: “All too often, short film scripts are treated as compressed features, with a form akin to a squashed up feature. Usually, there is a slavish adherence to the three-act structure of Aristotle's dramaturgy. The short film should be completely different.
“Generally, it is accepted that the most effective short films concentrate on a single main character and explore through a single sequence of events, his or her internal conflict. At the same time short films have to be visually strong enough to reveal that internal conflict, driving the story with emotional action as much as – or even more than – mere physical action.
Linda Cowgill, “Writing Short Films”: “Part of what works in a short film is subverting expectations that are based on our understanding of Hollywood's three act structure. In every good film the first act “sets up” the problem for the protagonist. Often what happens in the short film is that the problem is answered and solved in the middle of the story and the second half of the film deals with the ramifications of solving that problem.“
Screen East – Rough Guide to Writing Shorts
Creating a Short Film: Because of Mama
The Criterion Collection: A Look at Short Films
British Short Film Makers Page
Short Film Screenings
Writing Short Films - Linda J. Cowgill
Writing the Short Film - Ken Dancyger, Patricia Cooper
Writing Short Scripts - William H. Phillips
Producing and Directing the Short Film and Video - Peter Rea, David K. Irving
Making a Winning Short: How to Write, Direct, Edit, and Produce a Short Film - Edmond Levy