You wake up in the middle of the night with a great idea for a film, but you’ve never written a script before. Over the next few days the idea keeps eating at you. Suddenly you can’t contain yourself any longer. Where do you begin?

You can quickly grasp the format by buying the book of a screenplay. It looks deceptively easy and can be boiled down to three simple requirements: action, description and dialogue. A scene goes like this: 1. Int. Jane’s room, morning.

Jane eyes the dusty typewriter.

Jane: I have a story to tell and you’re going to help me tell it.

Sunlight slices the lace curtains. The typewriter glows.

Cut to . . .

There are some rules. The running time is estimated at about a minute a page, so your 110-page script will be nearly two hours long. A director can be daunted by a script which feels too fat. It means the shooting schedule will be cramped, and some scenes will have to be cut. A 90-page script feels good, as there will be time to develop more elaborate shots and it won’t be necessary to rush the actors. So, write economically.

One school of thought advises you not to write a word until you have worked out the story you want to tell, possibly sticking a series of plain postcards on your wall to chart the main action from beginning to end. This gives you a structure, so you won’t get lost. Another says that, once life is breathed into a character, the character starts wanting to do things you could never have predicted.

An American script tutor at film school used to tell us: “Sit down at the typewriter and open a vein.” If your story has power, it will soon start to obsess you. You will experience days of elation and days of stagnation.

You always have to give the audience a certain amount of information, and in a drama this can easily ring false or be boring. Exposition can be more digestible in a scene of conflict or tension. If a scene seems dead, cut into the action late. Get rid of that first page of dialogue and imagine how the scene would play out if you came in at the middle, or near the end. Or you can use the “What if?” technique. Ask yourself what would happen if, say, the woman rather than the man performed a critical action. Turn the tables; try to surprise.

When my brother Billy and I were writing Small Faces, we had a scene where the young Lex has unintentionally betrayed his own gang resulting in the murder of their leader at an ice rink. We said, “What if, instead of their leader, it is Bobby’s brother who is murdered.” This proposal instantly raised the stakes and, in the long run, demanded a more heartbreaking ordeal for Lex.

One of the most distinctive screenwriters I know is Jimmy McGovern. The dialogue punches away at you; he writes only the essential description, but he tells you the images which belong in the scene. With this combination of image and dialogue, he creates energy and rhythm. Actors love this kind of writing.

A storyboard is an extension of the script. Looking at storyboards can give you a sense of how the director and cinematographer will transform your text into images. But the storyboard is another transitional step. Nothing is fixed until it is caught on celluloid. This is the magic of film-making. So many people sweat for months preparing the film, then end up trying to capture the magic in the midst of a crisis, in two takes, in failing light, in a thunderstorm, with an actor who has twisted an ankle. And none of that was in your script.

You are not writing a novel, but a blueprint for a story told in moving pictures and sound. You are involved in a collaborative process. There will eventually be a whole crew of people interpreting the screenplay - production designer, costume designer, photographer, actors, director, and so on. This liberates you, the writer, from having to go into too much detail. Get to the essence of your story. Don’t spend too many lines describing the curtains.

While you’re writing your script, try to enjoy it, because this is the moment where you still have control over your own destiny - at least for the first draft. Through subsequent drafts, if luck holds and you get that far, more and more voices will be humming in your ear - the producer, the director, the financier. If you are fortunate, the voices will be wise. If not, there are strategies you can employ - deception andor belligerence might work where reason and persuasion have failed.

Sooner or later you will need to find a producer, who will try to attract a director and finance. If you don’t have an agent, you can send your script directly to any film production company. You may want to protect your copyright by sending a sealed, post-dated copy to yourself, though I believe it is rare for a UK company to steal someone else’s idea.

Most production companies hire readers who will write a report on your story, so you will need to pay attention to the opening. If you catch the reader’s interest in the first 20 pages, you have a chance. But even if you are refused, consider any advice offered and keep at it. Remember, the reader could be a moron, who will cringe when you receive your Oscar.

If you do start to write your story, you had better love it, because it won’t be a glamorous life. You will have to harden yourself against criticism and rejection, the staple diet of the artist. It helps to be tenacious, determined and enthusiastic, because it will be frustrating work. But it will also be great fun and can be incredibly rewarding.

It’s a mistake to think that nobody will be interested in a script by an unknown writer. A great script is rare, and everyone is looking for it. It is the foundation for any successful film. My agent advises me I may have to read 100 before I find one I love.

If you ever get your movie made, don’t expect the spotlight. The writer is usually the guy in the glasses whom no one notices. When we premi red The Playboys for the Goldwyn Company, at an LA cinema, I arrived in a limo with the two writers. We came down a red carpet into a barrage of photographers, but not a single camera flashed. They were looking for actors. I grumbled, only to be told, “Serves you right for entering with the writers”.

Gillies MacKinnon has directed several films, including ‘Regeneration’. He has just completed post-production on ‘Hideous Kinky’. The screenplay was written by his brother, Billy MacKinnon, from the novel by Esther Freud. It stars Kate Winslet and will be released later this year. Stills in the illustration are from ‘Small Faces’