What are your favorite books? Do you lean toward a particular style, such as young adult, romance, historical, sci-fi, murder mystery, psychological thrillers, or westerns?
I don’t necessarily agree that you should always write what you know, but it sure helps. How many authors today actually have been bitten by or have fallen in love with a vampire? How many have been to space? How many have been serial killers. The point is you have a good starting point for your writing if you read novels in the genre that interests you most.
Personally, I read a lot of historical novels, especially those set in the years preceding, during, and subsequent to the medieval period. Most of those novels are set in medieval Britain. So, when it came time to attempt my first novel, it was a no brainer. I already had pictures in my mind about what the land and villages looked like. I had a good idea of what the people wore. I knew how they traveled. I understood a bit about their religion. I knew certain details such as destriers being favored by knights as war horses and palfreys were calmer horses well suited to female riders.
I still do a ton of research to get the details right, but the general feel of my medieval world is well set in my head. I still look up everything from which herb cured a cough to what their shoes looked like. Because I have immersed myself in historical fiction for so many years, I’m quite comfortable in that world when I write about it.
So, now what? Stock your summer reading arsenal with the genre that you’re currently writing. You’ll learn so many nuances related to what the people talk like, how they behave, what they eat, where they travel, and so on, that your own writing ring truer. Then, get back to your computer and Write away!