write what you know. Of course, if you're writing a romance you may never have experienced hours and hours of mind blowing sex. Or if you're writing fantasy you might not have a wand or a book of spells at your disposal. That part you might have to make up. But you can use everything else you know. Like how scared you are of the dark or the nightmares you've had or the excruciating pain you felt when your dog came barreling at you at ludicrous speed and took you out and sent you to the emergency room. Every wound you ever had, every bad experience, every slight, every kiss. They are grist for your fodder. Use them.