If you have considered writing for the Black Libary (Games Workshop’s publishing arm) then Gav Thorpe has some useful tips for you at his blog.
Black Librayr are one of the few publishers who open advertise for new writers. However the process is quite specific: they want a 250-word sample of your writing. It is this sample writing that Gav addresses.
In the Grim Darkness of the Far Future, There is Only War. It’s a mission statement, not just a tag-line. Your piece has to involve some fighting, or some consequence of bloody war in a fairly direct fashion.
Gav also has a tip for anyone submitting in the near future:
Learn about Age of Sigmar. Really. I would wager that 80%+ of applicants are well-versed in 40K lore only. If you can be an expert on the unfolding Age of Sigmar setting, you’ve jumped a big chunk of the queue.
You can read the full article here.