I've heard many times from other writers the suggestion that we should write what we know. That makes sense to me since it has to be far more difficult to try to write about something you know nothing about. That usually means lots of research. But since I write, in my literary novels and collections of short stories, about the human condition based on people in my life or from my past, I would recommend that you might want to try something else. Try writing about who you know. And sometimes it takes just one incident about someone you knew from your past that left a deep impression on you and you've got a story. Your imagination will usually fill in the rest. This is where memoir writing meets fiction. 

When you think about it, writing a story about who you know makes sense since we usually have a main character in every story we write. You always need a 'who' to write about. Once you have the who you can then build a world around them. And if you have a particular character in mind from your past, you may already have the story you want to write. For example, in my late teens I worked with an interesting group of people. I have recently been working on their stories, or the little I remember about them, and often all I have is one or two memorable incidents and I'm working on a collection of short stories. I have had enough real life experiences to take those one or two incidents and build a world around each character.