"Most of us only find our own voices after we've sounded like a lot of other people." -Neil Gaiman, addressing the University of the Arts class of 2012
I spent a lot of time sounding like- or more often trying to sound like- others. As Mr. Gaiman went on to say that's not necessarily bad. It's natural to emulate those you admire.
That can be a great learning experience. It's good to try on different styles. It's good to try on different personas, to try to think like others. But just as in real life we need to learn who we are and live that life, we need to find our voice in writing (or painting or music or motorcycle design or whatever), and communicate with the world using that voice.
In the 4th grade I wrote a poem that was all mine. But I spent much of the 5th grade taking notes on people (a la Harriet the Spy) and trying to write comics (DC superheroes and Sgt Rock). In the 7th grade I was coming up with one liners like I found in very funny books by Art LInkletter, Richard Armour, and Alan King. Later I tried to write like Tolkien, and like Asimov, Laumer, Schmitz, and other authors from the golden and silver ages of SFF.
Eventually I started writing in my own voice. I don't recall a conscious decision to do this. I think it was more of a decision to try new things, to experiment, to go where I had never gone before. As it turns out, I found a number of voices, all mine. This comes in handy both for delineating characters within a story, and for switching genres. I don't want my children's stories to sound like my YA fantasy to sound like my mysteries to sound like my science fiction.
So play with the voices in your head, whether they belong to someone else, or simply you. But eventually you should hear more from you than anyone else. There's only one J. R. R. Tolkien. And there is only one you. Speak to us from the depths of your awesomeness.