“Write what you know” is one of the most misunderstood pieces of advice to new writers, probably because it’s often comes without much explanation and usually given by people who don’t know any better. They’ve read Louis L’Amour, Jack London, Ernest Hemingway and believe the only way to get the feel and accuracy for any topic is to have lived the life of your protagonist character. While traveling the world and living the life of adventure is great, it’s not very practical for the average writer. Fortunately, we have other resources to achieve that verisimilitude that would give even the most anal expert pause.
Interviews are a great source of information, especially for that special nuance that makes your world believable. Need to know something about a specific occupation, ask someone who does that job. What do employees call the drive-thru window station? What does a trucker mean when they, “hit the binders?” This is gold that will make your characters real and come alive. Writing about events in the past? Talk to relatives, neighbors, people who’ve been there. They’ve already done the grunt work.
Books. Histories. Biographies. Travelogues. Not only are these wonderful sources of information, but look great in the bookcase for that author photo. If budget is a problem books can be found relatively cheaply at yard sales and the bargain bins in bookstores.
Of course, there is everyone’s frenemy, the Internet. Just be careful when using such sites as Wikipedia. It’s a great resource if you need a quick fix or confirming what you already knew, but if it’s a major plot issue try for at least two sources of corroborating evidence.
In short, sure a PhD might be helpful, but it’s far from being a prerequisite to writing a good story. Just do some research. Then you will write what you know.