One of the great clichés of writing is to write what you know. By this, the cliché means use what you are familiar with. Many people have criticized this saying, insisting that one cannot grow as a writer without branching out. That writers should use their imagination. These aren’t invalid complaints. But it shows that such critics don’t necessarily understand the cliché.
Simply put, writing what you know is advice for new writers. You must walk before you can run. [How’s that for a cliché?] From an early age, we are taught that. Remember early grade school assignments about what we did for summer vacation? By writing about the familiar — and one hopes it’s about something we like — we are not only more likely to enjoy learning to write, but we are freed up to concentrate on the language arts. When working on your first story, it is the same. By fictionalizing something familiar, you are freed to learn the writing basics. Once you have the basics, the familiar then makes it easier to learn about plot, character development, and background. Only when you have mastered all this should you be branching out and writing stories that require either research or a great imagination (or both). World-building comes with experience, and shouldn’t be what you immediately jump into.
On the subject of imagination, it is worth noting that some writers don’t have a great imagination and never learn it. They stick with what they know, sometimes to extremes. One popular romance novelist made all her heroines a nurse, and all her heroes a Dutch doctor. Literally dozens of books. Why? Because she’d once been a nurse who married a Dutch doctor. The formula is the same, yet plot and character details differ. Despite the similarities, though, she was a beloved and best-selling author.
There are also practical reasons for writing what you know. Even in fantasy/sci fi, a writer should be aiming for realism, to make the reader feel like this could be a real place, with events that could actually happen. In cinema, filmmakers usually film on location to help achieve this, because studio sets just aren’t the same. And actors respond to that. It makes a difference. So too should writers aim for this. If you are rich and successful, you can simply visit your setting for a few weeks or months, and immerse yourself in the experience. Many writers can’t afford that. And doing research and writing from that is the writing equivalent of shooting a movie on a studio set. It may all be factual, but it is missing something indelible that will show up to the viewer/reader. Have you ever read a book where you got the impression the writer had never been to that location, despite giving a lot of small details about said location? I certainly have. Until you have the experience and know-how, it is better to write what you know than go out on a limb and screw it up. Give yourself time, patience, and above all experience, for creative world-building.