Consistently in research about writing and learning to be a better writer, I have found, and likely you have found, the term “write what you know” comes up. Steven King has made many books and short stories where the main characters are writers. The books he writes are primarily grounded in Mane. Great examples of being successful writing about what you know.
With our information-driven society, we all have the unique opportunity to learn and know more. You may have never build a house or even owned a home but maybe for your plot, you’d really like to have a character have a problem with their home that drives the story. A pipe burst and they find something in the wall. But you need to have the character repair the wall. You can do research. You don’t have to know every detail about something to write about it. Most tasks benefit from a 10,000-foot view instead of an intense detail.
Personally, I really like learning about serial killers, animals, psychology, and history so when I write I pull from that knowledge. If I need to deep dive into addiction (as example) and the effects of withdrawals on the body or the treatment of addiction I can research it. There are thousands of articles about it online detailing what it’s like. Anything we don’t know can be learned.
One of the worst things people can do is have a character who’s supposed to know about a subject matter or be an expert and have that character know nothing about it. A soldier who just fires a gun in some generic way. No, that gun is an AR 15 and this is how it’s reloaded or this is how it’s cleaned. This is why this is the gun that this character uses. If those topics fit into the story. Details are plentiful and gathering knowledge to create those details has never been easier.
If you make up an item or a gun you can add details to it by looking at history or current objects. A phaser gun might have some similar parts to it that current guns have. Your fantasy novel may have a great story but lack in a world. By looking into the history of regions and how things played out in reality you can take interesting events and create a story around them. The war of the roses is cited as being the inspiration for A Song of Ice and Fire. The red wedding is based on a real event.
Write what you know. If you don’t know find out enough to make it look like you do know. Fake it until you make it.
I write eBooks. You can read a few of my shorts here.