Author Diana Wynne Jones knows all about life in mystical and magical other worlds. For more than 20 years she has been creating unusual settings in which to set her books, such as The Lives of Christopher Chant (HarperCollins pound;4.99). As an Oxford student she attended lectures by those masters of other world creation C S Lewis and JRR Tolkein, and she says: “The best worlds are fantasy ‘if’ worlds. What if Napoleon won the battle of Waterloo or Guy Fawkes partly succeeded in blowing up the Houses of Parliament?”

She starts her recipe for creative writing “by putting two improbable things together. For instance, you could begin with a world where people ate curry and treacle pudding. Then you have to justify them. How did the two come together?” Next she moves on to the people. “The people are shaped by their history, so what happened to make them as they are? Is it an old civilisation or a new one?”

A fantasy world community is also shaped by its landscape, which has to be carefully thought out by would-be writers. “One very good way to get started is to make an enlargement of a map of your town and then name the places in it as if it were a country. Then you have to explain why the landscape looks as it does.”

Once you have charted your fantasy world, you have to ensure there is a rationale for everything in it. “You have to make sure that there are things like food and transport and things that logically hang together,” she says. While it’s easy enough for children to set a story in a primative civilisation or past era, she maintains that “you’ve got to follow it through, so you must remember the roads won’t be very good. There are certain key aspects which you need to work out. Climate is one, because it influences everything.” This is important when it comes to considering how your characters may find food or drink for instance. It is also something Diana has had recent experience of as her latest book, The Merlin Conspiracy is based in a desert world.

As well as considering major issues such as religion and customs, she says writers should also pay attention to minutia. “One of the things that annoyed me intensely about most of the Tolkien imitators,” she says, “is that they’ve forgotten and left out all the animal population and the insects. Names are quite an important part of your world - they set the atmosphere - and so is the language.

“You could start with any of these aspects, provided you bring in the others as well.

“Then you have to decide the degree of magic or otherwise - whether it’s going to be a completely mundane real-life type of world or whether you are going to have lots of magic.

“Magic has to have its own rules, just as the land does. Each land has its own kind of magic, which works in a certain way. There are about 1,000 or more types of magic. You can’t do them all in one world. There’s the slightly sentimental type - fairies and gnomes. Then there’s the ‘click your fingers and wave a wand’ type... There’s runes and chanting, generally very boring, which I don’t use that much.”

One final tip to budding fantasy writers: “You have to know far more than goes down on the page and the bits that don’t get in are just as important as the bits that do. People feel they’ve got to get it all in because they’ve made it up but what you want is an active piece of action that’s going on in a different place and time with different customs to your own.”

Diana Wynne Jones is the author of more than 20 fantasies for children and adults, including The Chrestomanci Series and The Tough Guide to Fantasyland. Her latest book, The Merlin Conspiracy (HarperCollins pound;12.99) is published this month Curriculum link: NLS Y1 term 3, Stories about fantasy worlds