The phrase most spoken in creative writing groups and classes is; ‘write what you know.’ I’ve never fully subscribed to this assertion.
I don’t think Terry Pratchett had much experience in flat worlds atop enormous turtles and I’m quite sure that Douglas Adams had never hitchhiked through the galaxy and yet they both wrote legendary books set in those very worlds.
There is a kernel of truth in the advice though; when it comes to emotion, any emotion – write what you know. Or, more accurately: write what you feel.
Emotion and the way you convey it is where your unique voice lives. Emotion is how you truly strike a chord with your readers. It goes for any and all emotions: love, anger, pain, hurt. The way you write emotion will bring your characters and your story to life in a way (if done well) that will resonate with your readers.
‘Write what you know.’ that phrase, when boiled down to what it should really mean is simply ‘be honest.’
So, what should you write about? Absolutely anything you can conceive of. That’s the most beautiful thing about writing fiction. You can do whatever you want; journeys through galaxies or trips to upside-down fantasy lands and – if it’s honest – it might be brilliant.