"Write what you know" is good advice, up to a point, but it also comes with its own set of perils and pitfalls. One of the big ones? When you are passionate and knowledgable about a topic, it's easy to forget that not everyone shares your particular obsession.
I was reminded of this the other day while reading notes from a Trusted Reader. The short story I sent him presupposed a knowledge of 16th century Scottish/English politics, the basic vocabulary of the Scotts dialect, fairy folklore in general, and the stolen child/changeling trope in particular. This Trusted Reader is exceedingly intelligent, but his knowledge base contains none of those things. Which, in a very important way, made him an ideal reader for this tale.
Which brings us to today's writing tip.
If your story is deeply rooted in a particular field, be it forensic medicine or Major League baseball, it will need to make sense to someone who isn't a pathologist or a pitcher. When you know a subject very, very well, you may not be the best judge of whether you've provided adequate background for someone who doesn't. A reader who isn't familiar with one or more of the story's key themes and elements comes at the story very differently than you do. If something is confusing or unclear to him, you need to expand or clarify. He's also more likely to see how the story works apart from the knowledge-specific references. Someone who's not distracted by the minutia of folklore or Star Wars or coin collecting may see big-picture plot holes and character inconsistencies that are less visible to people who live and love the details.
I'm fairly new to the practice of sharing with Trusted Readers. For years, the notion of anyone reading anything Before It Was Ready was the sort of thing I contemplated only during nightmares. The kind of dream where you forgot to study for an exam, or you have to perform a piece of music you've never practiced and can't sight-read because the score is nothing but blank paper, or you're in a shopping mall during the Christmas rush and suddenly your clothes disappear and oops, there you are. Giving someone a first draft to read feels a lot like those dreams. It's way, way outside my comfort zone, but it's worth doing. I'm pretty sure that if I'd started earlier, I'd be a much better writer today.
If you're a writer who's not ready to take this step, or who has yet to find Trusted Readers, writing what you know for people who don't can be a challenge. In the first draft, you can splash expertise onto the page or screen until it looks like a Jackson Pollack painting, but when you're revising, here's a tactic that might help: Bring to mind a friend, family member, or acquaintance--or an imaginary Ideal Reader, for that matter--who knows very little about the topic or the setting or the magic system, and try to envision a passage as it would appear from his point of view. If it leaves him scratching his imaginary head, you've got more work to do.