When I first started writing, I worried about this endlessly. How did the writers I liked get their stuff and how could a no one like me get my own? Years later, I'm amazed that any of us need to ask about this. For the themes and ideas we're meant to use are really inseparable from our own lives. Don't confuse that with writing your autobiography--which no one except your family will really want to read. But the images and themes that should be the soul of your writing are concentrated essences you simply can't escape from and shouldn't bother to try: core memories and lessons and dreams and regrets that are uniquely and naturally you.
Here are 2 personal examples to show you what I mean:
1) Born in the US, I lived ten years in Canada as a stateless person, intending to become a Canadian citizen. Bad mistake, I came to see. After a years-long struggle, I was able to go home with a Green Card because of a family petition. Five years later, I became an American for the second time. I tried writing an autobiographical account about my experience. But because it was all about Me and everything I'd been through, I couldn't bear to edit it and it ran on for 600 pages. Almost every U.S. agent praised my writing style...but said the book couldn't be sold.
I despaired...till I started to wonder: What if I re-created the essence of the story...as a horror novel? A transplanted American who's become Canadian finds and steals a haunted suit that begins to change him into its dead owner. The book became The Suiting. It won me an agent who sold it to Tor as part of my first two-book contract. A Stoker Award followed, then a small option for film. And this came about because I'd stopped looking elsewhere for ideas and also stopped thinking of Me. I'd learned to translate an essence into narrative lingo the readers could get.
2) Today I spent happy time pre-applying for Washington Enhanced ID. More time on the phone setting up an appointment. But I never thought of this as drudgery. Since returning to the States I've always been obsessed with having the proper ID--as if with every move I make I reprove that I'm American. And I also realized today that every book I've written concerns, in one way or another, a stranger who's in a new land...and must fight to establish his spiritual ID.
My best advice on the challenge is this: don't look harder, or further outside yourself, relax into your history--and you'll find all you need right there.