The generic writing advice for the novice always insists you must write what you know. Balderdash. If you studied at Cambridge or Oxford in the early 20th century you were expected to write poetry, essays, memoir, fiction and literary critiques. You studied language, the classics, read the Greeks and Romans in the original to prepare you for the challenge of putting your thoughts, ideas and imagination on paper. The task of writing was one of engaging the reader on any subject. What mattered was your originality, use of language, imagery, the specificity with which you developed a scene or idea. These requirements applied to all forms, from food writing to an examination of social mores. You didn't try to wedge yourself into a particular slot as we do these days. We call ourselves bloggers or YA authors. At university they called themselves writers. If you don't know how to tackle a form, you can learn. You may not master it, but that doesn't matter. The process of challenging yourself is what counts, the lessons you learn, either about craft or yourself.
We refer to creative nonfiction as though it is a special category when all writing by definition is creative. Writers love language, story, characters and ideas. If you develop your facility with these elements of writing, you increase your range as a writer regardless of the genre you prefer. Writing a poem sharpens your imagery in describing a scene. Writing a biographical sketch of a family member enlarges your compassion when creating a character for a story.
When was the last time you attempted a piece of writing that challenged your skills? Perhaps you are most comfortable writing fiction or travel pieces for adults. You might be amazed at what comes forward if you develop a critical examination of the essays of Montaigne or a story for toddlers.
I hear people say they don't have time for anything but their current project. However I encourage you to devote one of your daily 15 minute writing sessions to trying something new each week. You would be amazed at the dividends this investment in your craft will pay when you return to your ongoing piece.
Once you have finished this new effort, I also challenge you to send it out for publication or put it on your blog. This will help you take your new writing seriously. If you've never written a poem, read them for a week (of course it takes a lifetime of reading poetry to crack that code--but start with a week's worth of poems). Then create a poem. You don't have to show it to anyone if you are self-conscious about it. But it is far better to submit it to a review site for a critique.
Of course I am practicing what I preach. I am halfway through a children's story and I know nothing about connecting with a young reader. I've written half a dozen poems I would never show to anyone, but have new respect for the power of an image. Memoir terrifies me, yet I am learning to expose myself on this blog more and more. I finally said the D word, and I cannot tell you how difficult it was to expose that sad chapter of my life. Yet I want to connect with my readers, many of whom also struggle to write when their marriages, health or life circumstances unravel. Yet, this does not mean I have given up on my first love, the novel.
See yourself as a writer, not as a genre writer and expand your gifts and skills. The experience doesn't have to become an everyday effort, but it will pay dividends for a lifetime. Once you've learned something, you can't unlearn it. Good luck.