Imagine it: the house lights go down and silence falls in the auditorium. There is a pause, expectancy is high, the lights come up, an actor enters, he opens his mouth and ... your words come out. A figment of your imagination is brought to life, your dreams and ideas are made real; they are breathing, tangible, just a few yards away and the audience listens, watches, believes. No one suspects that you are you, that you are the one who gave life to these characters.

You sit there, exhilarated, hugging your secret, knowing what is to come. To have a play performed is a rare and wonderful privilege. It is worth all the lonely agony of writing - the set-backs, the arguments with directors, the frayed nerves. If you have even toyed with the idea of writing a play, I urge you to have a go.

Here, in three acts, are some points to bear in mind.

Act one. Prepare. Go to the theatre. Do not mistake theatre for television or film. The only way to grasp its unique qualities is by going and experiencing it. There is an element of magic in theatre. Each performance of a play is a happening. The words may be the same (if you’re lucky) but the performances and, moreover, the audience, won’t be. Atmosphere is everything. Once the lights have gone down, people will suspend their disbelief. Use this. As a playwright, you can create any kind of world you choose. It can be close to, or distant from, the real world. As long as you believe in it, everyone else will.

Go and see the same play twice. If you have enjoyed and admired a play, go and see it again. Try to sit back from it and analyse the way the playwright has set up the characters, engaged the audience’s emotions and taken them through the story.

Research. If the idea for your play is set in a different world from the one you inhabit, if, for example, it is set in the 17th century or in the world of sumo wrestling, do some thorough research. It may be that you eventually disregard 90 per cent of what you learn, but it will certainly hold you up and cramp you if you feel there are gaps in your knowledge, and some of the details you pick up will spark your imagination and become invaluable.

Plan ahead. It is difficult to say how much of the play you should plan before you begin to write. All playwrights differ. Being a control freak, I plan virtually everything. Others say that they just sit down and write and then start to shape what they have produced. If you wish to plan, any or all of the following may be useful: Define why you want to write this play. What is the central idea, the touchstone? Do you want to make a point about the human condition? Do you want to ask a question? Do you want to challenge? Do you simply want to make people laugh or to tell a good story? Write down your thoughts on this and pin them up on the wall.

Write studies of your characters so that you know them inside out. If you are basing them on people you know, how are they the same as them and how do they differ? Pick a subject and write about it in the way that character would speak, so that you feel familiar with their voice, their rhythm and their turn of phrase.

Write down a rough idea of the plot. Where would you like your characters to get to by the end of the play? Having said all that, don’t over-plan. I always leave a small area of mystery. With luck, the play will take on a life of its own and judging when to go with it and when to rein it in is all part of the challenge.

Act two. Write. For me, the only golden rule when writing a play is to set up dramatic tension. All other rules are there to be broken, but without dramatic tension, a play will not work. At its simplest, dramatic tension can be created by one character wanting one thing and another wanting the opposite. For example, in Miller’s The Crucible, Danforth wants Proctor to sign his name to the confession of witchcraft. But Proctor would rather do anything than sign.

Or, it could be that the tension is created by two people wanting the same thing, but one fighting against that want. For example, in Shakespeare’s Macbeth, Lady Macbeth tries to overcome Macbeth’s fear of killing the king and gaining what he wants. Will he do it, won’t he do it? It is not always as obvious as this.

It can be that characters disguise what they want very well. On the surface a scene may be harmonious, but the audience must sense that there is some kind of power struggle going on underneath. The ways in which dramatic tension can be created are innumerable. But always ask yourself where the dramatic tension lies in what you are writing.

A scene which is simply getting plot information across or illustrating a particular facet of a character will be a boring scene. Let the play dictate its own shape - don’t feel you have to have acts and scenes if they aren’t useful. It may be that the play is one line of continuous action, set in one place.

In theatre it is usually better to show rather than refer to action. An audience will take in information more readily if there are visuals to support it. Resist talking about characters before the audience has met them, unless that character is the protagonist or represents some kind of threat and you are trying to build dramatic tension. Make sure the characters’ names are used quite early on and that the relationships between the characters are clearly established. Don’t allow dialogue to become completely linear unless you are making a point using this technique. Non-sequiturs are more common in life than straight answers, and we often don’t listen to what someone says but follow our own agenda.

Keep imagining your writing being performed. It is not a novel. Act it out using different voices for different characters. Stick at it. It may be heavy going at first, but the work will only gain momentum if you do it regularly. Before you know it, you’ll be on a roll.

Act Three. Get your play performed. Once you have written and rewritten your play and are reasonably confident about it, there are a number of routes you can take to getting it performed. You could enter it for a competition. The Mobil Playwrighting Competition is the most prestigious. A winning play is often produced by the Royal Exchange Theatre in Manchester. You could enter it for an award, such as the Allied Domecq Award, run by the Bush Theatre or the Verity Bargate Award run by the Soho Theatre Company. Winning either of these is pretty well guaranteed to lead to a production.

You could send it to a director whose work you admire, asking them to read it. If you don’t know how to contact them, try sending it to the last theatre they worked for and ask for it to be forwarded. You could try sending it to a local theatre, although many cannot afford to mount productions of new work. Ring them up and ask them what their policy is. A better idea might be to send it to the literary manager of one of the theatres which specialise in new writing and have a whole machine in place to nurture new talent. These include: the Royal Court, the Bush, Hampstead Theatre and the Soho Theatre Company - all in London. It may be a long time before you hear from anyone. But the last four mentioned should at least, in time, send you a reader’s report with an honest response and some tips on improvement.

Productions of unsolicited scripts are rare, but I honestly believe that if someone writes a very good play it will eventually be performed. I wish you luck.

Helen Edmundson’s most recent work includes The Clearing, produced at the Bush Theatre, which won the John Whiting Award and a Time Out award and an adaptation of War and Peace now at the National Theatre.

Next week: Lavinia Greenlaw on writing poetry