The most important aspect of writing is voice: that feel, sound, or signature thing that makes a piece identifiable as a particular writer’s work. Inevitably a writer just starting out will copy a mentor’s voice — subconsciously or not — to start understanding what makes it interesting. Then, through craft, experience, more reading, more experimenting with different mimicry, the writer begins to sculpt a signature vibe. Because it can only develop through careful, calculated practice, true voice may take years to articulate.
Read some of your own juvenilia; does it sound different? odd? bad? not like you? Most likely, that old writing was not crafted with your current voice. Note that your writing will change slightly, as does the way you speak: maturity, lifestyle, location, all will creep in. But this is honing of your voice. This application of life differs from the first stages of development. Early Hemingway (or King, Munro, Yeats, Garcia Marquez, Alexis, Doolittle, McCarthy…) has a different feel than later Hemingway, but the voice is there, loud, clear, identifiable.
Read. Read again. Read something different. Read something you dislike.
Write. Write some more. Write in a style you aren’t used to. Write in a style you detest.
Although the intangibility of voice can be frustrating, the importance of voice is paramount. When writing, ask yourself: what makes the story yours; outside of physical detail, could someone identify it as yours; what could you add, change, delete, to make it more yours? Eventually all these mechanics, these nuances will start to flow naturally, giving life to your own inner rhythms, rhymes, metres, in the form of voice.