Below is a short and concise - but hopefully useful outline on how to write a script. It is by no means comprehensive and is a mish mash of various teachers' and theorists' ideas and work. See this as a simple crash course. Hope it helps. Here we go...

Writing a script (especially a feature length one) is not as easy as many seem to believe it is. Compared to the novel or traditional prose, the script is a unique animal. Ultimately most see a script as not a thing in itself but rather like an architect's plan for a building. In the same way that a building's plans are not the building itself - the script is ultimately an aspiration towards making a film. However increasingly scriptwriting is being considered by some as an art unto itself and one that is often read and appreciated regardless of whether it is produced or not.

There are a considerable amount of rules and conventions you are expected to follow when writing a script. Some are annoying and some are downright stupid. But if you want to have your script read you should try and follow as many of these conventions as possible. Script readers, commissioning editors and producers who have an intimidating pile of scripts on their desk tend to first throw "unconventionally" formatted and styled scripts straight into the dustbin without even reading them. To them this is a time saving way of weeding out the amateurs from the professionals or serious writers. Never make it obvious you're new to the game - even if you are.

Many of these conventions are largely based on Classic Hollywood Realism - the style of the vast majority of American films. But even if your script is to be the ultimate surreal, Dadaist, art-house experience, conventional wisdom tell us that it's nevertheless useful to learn these "rules" anyway. The logic is that you've got to know the rules before you can subvert them.

THE PLOT
The first thing to do is to work out what your script is going to be about. This is your business so figure it out yourself. (Although bear in mind what is written below because it does impact in the type or idea you will want to develop). Then you need to create a plot - i.e. basically what happens in your story and in what order.

The traditional Hollywood script plot structure is often called the three-act structure. Another way of looking at it is what I call the "balance-imbalance-balance" concept. These concepts work pretty much the same - focusing primarily on a central character. The Balance/Imbalance/Balance structure works in the following way. (We'll call our central character "X").

 

1 - Balance: This is the initial state of your main character: X is a content dog trainer living with her dog Shoop. She avoids men because of previous affairs gone sour.

2 - Imbalance: A challenge or obstacle is foisted onto our hero which she undertakes to do something about. This changes her life: Shoop is stolen by a rival dog training company. Lonely and her spirits low, X spends her time searching for Shoop. She begins to lose customers as a result. Along the way she meets a helpful, sensitive policeman with buns of steel who embarks on the dog searching journey with her. Eventually she and Mr Buns of Steel track down Shoop and rescue the canine.

3 - Balance: Things are restored back to order but with something gained: Having rescued the dog, X returns to her life of contented dog training now with the addition of a well hung policeman in her bed. She has also overcome her fear of taking romantic risks. Together with the help of her beau her business has taken off like never before. Our hero has learnt something and gained from the experience. In other words, she has developed.

The most dramatic elements occur in the "imbalance" section. The challenge and what our hero does to overcome it is the "meat on the bones" of our story.

If I were to ask what X's primary challenge is, you might say that it is to find her dog. I might disagree and say that her primary goal is actually to overcome her loneliness and fear of men. In this way scripts can have different levels of meaning.

X's story could be a comedy, a serious drama and even a feminist comment on the way women are expected to conform to patriarchal society in which life without a man is seen as meaningless. It's your choice.

Now how does the plot become a script? Follow the easy steps below.

 

STEP ONE
Clearly write out your concept in a couple of lines: eg: "This movie is about "X, a happy dog trainer whose life is thrown into disarray when her faithful doggy companion Shoop is abducted by a rival dog training company." This sets out what your story is about as well as who your primary characters are. You should also try and figure out if this will be a comedy, a drama or horror story. This is called the "genre" of the film. (Producers need to know this or they get very confused.) However today we see more and more mixing of genres in the same film. No dialogue should be added until STEP SEVEN

STEP TWO
Write a paragraph outlining the story in a little more detail - this time adding in a few more characters and important events. Get a stronger feeling for how the thing will play out. We find out X has actually been rather lonely, we learn that there's a hot policeman in there too and there's a climatic shootout towards the end when Shoop is rescued. One could call this paragraph a short synopsis of your story.

STEP THREE
Write a longer outline of your plot. Depending on you, this can be anything from two to twenty pages. (You can also break this step into more steps and write increasingly longer outlines before proceeding to Step Four.). This pretty much establishes the basics of your plot and many of the twists and turns that may take place. Some also call this the "beats" of your script. You can add in stuff about the bad guys, who they are and their motivation for their actions.

STEP FOUR
Take your long outline and begin to break it up into one-or-two line paragraphs. Each paragraph should be a particular unique event. Eg:

What once was:

  "X is woken up in the morning by Shoop's long tongue in her face. Later X drives to her dog-training school with Shoop panting in the back."

Becomes:

 

Paragraph one: X is woken up in the morning by Shoop's long tongue licking her face.

Paragraph two. X drives to her dog training school with Shoop panting in the back.

STEP FIVE
Fill in more paragraphs to make the story flow well and add any other paragraphs needed to fill out the story and expand elements that need it. The paragraphs should include more detailed actions on how things happen.

STEP SIX
Turn these paragraphs into scenes. The concept of a scene is very difficult to explain and almost needs to be intuitively understood. I've never seen an adequate explanation or definition to-date. It helps a great deal to read as many scripts as possible to get a feeling for this. Nevertheless, roughly, a scene is an event that happens in a unique place and time. E.g. The paragraph description:

 

Paragraph Sixty Five X arrives at the factory and after looking around discovers Shoop's dog leash in the bathroom.

Could be broken down into:

 

EXT. ABANDONED FACTORY. DAY X looks up at the front of the abandoned factory. A sign atop reads "NUWARE TILES". X walks up to the front door and opens it.

INT. ABANDONED FACTORY FLOOR. DAY Walking through the dark factory building it becomes clear that there is no-one here anymore. Rubble and trash are strewn all over the floor.

INT. ABANDONED FACTORY TOILET. DAY X opens the door to a filthy toilet and looks in. About to walk away she sees something. A dog's leash. Bending down she picks it up and realises that it is Shoop's leash.

INT/EXT: This refers to the location of the scene. If it is inside it is INT (for interior); if it is set outside it is EXT (for exterior). This should be followed by the location e.g. ABANDONED WAREHOUSE.

DAY/NIGHT: This refers to wether the scene occurs in the day or night. This follows the location.

STEP SEVEN
Start filling in dialogue as well as more detail under each scene. You should have a first draft completed by the end of this process.

STEP EIGHT, NINE, TEN, ELEVEN etc... There's a corny but valuable saying about writing that goes: "Writing is not about writing - but about re-writing". The first draft will almost always be shit. It's in the refining, re-writing, re-plotting and fine-tuning that great scripts get made. Congratulations - you've written a script! Now wasn't that fun?

OTHER HANDY HINTS
Format
In order to gauge more or less how long a film a script will make (very useful for producers), there are certain standards in formatting. Avoid these at your own risk. Americans especially are very rigid about this. These standards allow us to measure a script's length by saying that: "a page of script equals roughly a minute of screen time". This is a very rough guide (often action films scripts are short but take longer on screen than a dialogue based script) and not to be completely trusted.

Font
You should use Courier (or New Courier) Size 12. This is a fixed-width font, which many believe makes it easier to read. You'll be surprised how picky some readers are about this.

Length
Should fall between 90 to 120 pages. Anything longer and your chances of being read begin to diminish. Dumb huh?

Numbering
Avoid numbering scenes unless it is a shooting script which will only be seen by yourself or when actually shootingthe film. Script readers don't like them.

Layout
A script layout should look something like this. Some will demand exact measured layouts but few are very sticky about exact distances from margins etc. (Note that it is difficult to display exact layouts on web browsers - this is only a rough guide.)

Layout Example

Dialogue
This one is a toughie. It's very hard to teach dialogue. One has to develop an ear for the way people really speak and not how we think they speak. Listen to people from various backgrounds and in various situations talk as often as you can. You'll probably notice that people are not very eloquent in general. They don't express themselves very well vocally and a great deal of what is NOT said is just as important (often more so) than what is said. Bring these thoughts to your scriptwriting process. And again read lots of scripts and watch many films to become more sensitive to dialogue.

An important thing to remember is that scripts are the basis of the visual medium of film. An old adage is: never say what you can show instead. In other words if a character is angry don't have her say "I'm angry!", show it to us. E.g. have her smash a window with a chair instead.

Characters
There is almost always a central character in a Hollywood movie. That is because Hollywood films work on the basis of the audience being able to identify with a character and his or her experiences. More than one central character tends to confuse the viewers (at least according to many studio execs).

Characters are expected to be three dimensional and rounded. By that it is meant that we should get a sense of their history and how it has affected them as well as understanding why they do what they do (usually called Motivation). (E.g. X avoids men because of a previous heartbreaking episode). This is based on the idea that we do things for knowable reasons. Modern psychology came up with this somewhat naïve notion. However we rarely actually have access to the full reasons why we, others (or ourselves) do what we do. Nevertheless Hollywood believes otherwise.

This convention often leads to some awfully contrived scenes in which characters reveal really corny back-stories and traumatic past events. This is also called "exposition" and is very difficult to write without being obvious or corny. Exposition should happen organically and without the audience realising it. Some filmmakers such as David Cronenberg don't allow us to get close to their characters and we rarely know why they do things except for the obvious. Unlike in most Hollywood films we are not participants in Cronenberg's films - but voyeurs watching the action from the outside.

Nevertheless it often helps to create back-stories for your characters. These are basically histories for your characters - their life experiences, social and economic background etc. This doesn't have to all be obviously present in the script but helps to craft more real characters.

Part of having a three dimensional character is that we see him or her develop across the course of the script. They should change in front of our very eyes. Again remember these are all conventions for a conventional style of film.

Camera Directions
It's usually not appreciated that you include camera movements in your scripts. There are ways of getting around this in sticky situations. Sometimes it can't be avoided. Tarantino's scripts on the other hand are full of camera directions. If the script is going to be pitched to outside producers and script-readers try and avoid it. If you are going to direct the thing yourself than go ahead and put them in.

The most useful advice I can give however is to read as many scripts you can lay your hands on - either on the Internet or at your local bookstore.