Well that's just plain wrong, isn't it? Write what you know? Personally, I've never been on a spaceship - does that mean I can't write science fiction? And I doubt whether Agatha Christie was a closet mass murderer or Tolkien had hobbits and elves at the bottom of his garden.
Flip it around. Know what you write. Now that sounds better. How can you write a convincing murder trial if you've never seen a court except in films or on tv? They only show you the interesting bits on television and not the hours of tedious apparently irrelevant questions designed to trip up a witness. I once spent an entire day giving evidence for the prosecution - it might sound exciting, but in reality it consisted of endlessly reciting serial numbers of pieces of computer equipment that I'd taken from a house somewhere during the course of an investigation. Presumably defence counsel hoped I'd get a number wrong at some point and they'd then try to convince the jury that all the rest of my evidence must be mistaken too.
But most courts are open to the public. You can sit in the gallery and watch the proceedings and hopefully write your novel with an edge of authenticity. The smell of the place, the tension, the expressions on the faces of the victims and witnesses. The old lady juror trying to stay awake, the coffee machine and the airport-style security.
So you can't find a local spaceship pilot to show you around? Then research. The internet is a marvellous tool - or cheat a little and see how other authors have done it. One of the best novels I know which describes spaceflight is Stephen Baxter's Ark. Although I was less than impressed with the shoddy formatting of this novel in its conversion to an e-book, the story itself is impressive in how Baxter describes spaceflight - both the physics and the more mundane aspects of actually living long-term in close confinement on a spacecraft.
Vampires? Or other paranormal creatures? They may not exist, but there is an accepted tradition now, certain tropes of the genre to describe their behaviour and habits. You can go with the flow and your readers will follow - or you can break out of the mould and take a new sparkly approach. You have a choice.
I've done some weird things in my life so far. I can accurately describe heroin down to texture, smell and taste. But I can do the same with horse manure and cow dung, having walked through the streets of Chester liberally coated in the stuff as a teenager (the Chester raft race still goes on. I participated as a teenager with the Wirral Sub Aqua Club).
And when all else fails, there's always imagination. Use it. Be there on that distant planet or that dark alleyway and your readesr will be there with you.