I’ve just had a read of a fantastic blog post outlining a lesson sequence to write historical fiction. You can read the full article at http://mrparkinsonict.blogspot.com/2013/02/epic-citadel-igniting-childrens.html
Although the author did it with Y5 students, the actual lesson sequence could work really well with older year groups. The key ingredient is a high quality, immersive, environment for students to explore prior to beginning their story. In this case he uses the game Epic Citadel. This is a free app designed to show off a graphics engine, but offers an incredibly detailed medieval environment for students to explore. If other apps exist that provide similarly detailed environments then they could be used instead. The later stages of the sequence could then be applied.