Show the developer up-front that you can behave professionally. Read the submission guidelines before asking questions. Try asking people on newsgroups or other sources before talking directly to a developer. Don't insult the developer. Get something published, even if it's just a short story.
RPG companies like to see prior publication credits as much as anyone else does.
Developers are far more interested in people who can write well than in people who know the game world inside and out. If you want to write for a game, concentrate on proving that you're a good writer, not that you know game trivia. Get lots of experience writing. I don't mean for your own website, and I don't mean for your friends. Get involved in workshops.