I must confess to not knowing very much about Diana Wynne Jones, but have been thinking about her this week with the news of her death.
This morning, I found a delightful little autobiography on a fansite devoted to her work. Highly recommended reading.
There's also a link to an article "Hints on Writing a Story" which offers all manner of wonderful, sensible advice such as "Most teachers will tell you that you need to make a careful plan of your story before you start. This is because most teachers do not write stories."