Let me give you the single worst piece of writing advice I have ever heard. Write what you know. You are boring, and I don't say that to be mean. You want to be boring! Drama sucks, fights suck! Car trouble, money trouble, getting robbed - especially getting robbed - SUCKS! For us humans, we're our most content when we're relaxing on the couch, sipping a drink, not a care in the world. But reading a book that way - That would be a snooze fest.
But many writers get caught in the trap of looking at their own lives and committing them to the page. I understand the impulse to want to do this. Working within your own bubble is comfortable and safe; you don't have to worry about research or getting anything wrong. This would be perfectly fine if you were writing a memoir or perhaps a technical document, but when it comes to fiction, it is absolutely crucial that you step outside your own box.
If I had to coin a better piece of writing advice, it would be this: Write what you can dream, research what you don't, but only in editing. If your book is a historical fiction, you might need to get at least the broad strokes of the time period and conflict, but much of the action, dialogue, and sequence of events can often be committed to the page with the finer details of things like when WW2 took place (1 September 1939 – 2 September 1945 by the way) happening later. Instead, use a placeholder [WW2 dates needed] so you can find them later (I quite often use programming conventions for this, like TODO: which tend to stand out among the text).
Many great works are written exactly like this. Tolkien certainly never visited Middle-earth, and Mary Shelley was a teenager when she wrote Frankenstein. If the greats had written what they knew, we'd have nothing.
Sometimes a little research is necessary to understand the topic or period you're writing, in a previous article, I spoke about understanding the characters you are trying to portray, for example. If you do decide to do research before you write, make sure the research doesn't become the tool to procrastinate. Way too many authors are seduced by the prospect of doing research; in contrast to writing, it is easy to do and feels like work, but ultimately it is a trap. Hours spent on research are hours lost that could have been used putting words on the page.
Ultimately, the reader has no idea what you don't know, and if you depict your scene convincingly enough, they'll never have a need to question it. If you're writing a depiction of an elf making a splint, as long as the process is close (which you looked up in editing) the reader will remain blissfully unaware that you're not a field medic.
There is a kernel of truth to the often repeated advice of "Write what you know," and that is, you should write what makes you emotional - be it what scares you, makes you happy, sad, or excites you. At the end of the day, you're the author. When you are ready to start writing your next outline or novel, pause and ask yourself if you're just writing an idealized version of your own world, or if you're daring to dream. And remember, the only difference between a dreamer and an author is the tap of keys or the stroke of a pen.
