"Write what you know." It's one of the oldest chestnuts in writing. (The oldest one probably has to do with grammar.) It's also not an easy thing to do.
Say you have a job in a patent office. (You poor bastard.) And when you write you write about the ins and outs of working at a patent office. You write about your crazy or not-so-crazy coworkers and the little stories that happen every day. You write about going home to your husband or your wife, maybe your kids or your dog, and the time you spend with them.
You write boring.
All that stuff isn't a story. The ins and outs of your job aren't narrative; they're probably a training manual. The little stories about your coworkers aren't gripping fiction; at best they're cute anecdotes, at worst they're going to turn you into a pariah and get you fired. The time you spend with your happy family is not interesting except to a genealogist.
"Write what you know" is not to be interpreted as "write what you do". You write what you feel.
You don't write about what you do at the patent office. You write about the bone-deep exhaustion you feel at eight in the morning because you were up too late again last night. You write about the panic of a deadline that's about to sail by, and the elation of nailing the bastard before he gets away. You write about the way a drop of blood looks on a TPS report after it slices your index finger open.
You don't write about your coworkers and the things they do. You write about the secret struggle for dominance between I.T. and the secretarial staff. You write about the bald spot on the back of Ed's head that looks like a smiley face, the glint of light on Olivia's lipstick when she walks just-so under the fluorescents, the purplish-red shade Donald's face turned when he gave his "exit speech" after the layoff.
You don't write about the daily events in your household. You write about the kick in the collarbone when the dog jumps onto your chest to lick your face. You write about the misting rain on your skin while you're applauding at your son's soccer game. You write about the warmth of an arm around your neck and a body pressed against yours, side by side. You write about broken dishes and screaming matches that rip your throat open and makeup sex that means you have to buy a new bed.
And you never, ever, name names. Names hurt, and anyway they aren't so important. It's impressions and emotions and thrills and sorrows and loves and hates that you want to capture, and you can never do that if you're afraid you'll hurt someone.
Write what you feel. You're the only one who can, because you're the only one who really knows.