Why do you write?
I write to change my world by revising and giving it a happy ending. I think most write fiction to create new realities and new ways of expressing ourselves. It gives us the power to fix anything we don't like in the real world. We write to escape, and to escape we must express ourselves in our writers voices.
Who do you become when you write?
First, you become vulnerable. You must become the characters, all of them -- even the bad guys. For the characters to be compelling I believe they must contain some real part of the writer's personality. You have all the voices inside you waiting to come out; they only need the right character. Being able to let them each speak for themselves, individually, is your writers voice. You literally must pour yourself into your writing. That isn't as much a cliche as you may have thought.
Have you ever found an old writing of yours, something you'd written a few years ago, and heard a certain voice that brought up emotions? It will have a tone of realism that could be embarrassing or pleasant, depending on the words and topic you chose, but it's your real writers voice. It is probably something you wrote on the spur of the moment while in a particular emotional state. Learn to control it by becoming each character. To become each character, you must know them well. Study them, make them individuals by basing them on someone real.
I've heard some creative writers say they don't worry about the characters, because they think the story is more important. They admit throwing card-board characters in as they're needed to get the story to the finish line. I haven't read their work so I don't know if they can pull it off or not, but I wonder who performs the action, how is emotion brought in? Even if it's completely narrated, the narrator still needs a strong voice.
I agree with the statement that the story is important, but the characters are at least equally important. Good ones can fool the reader into thinking even a bad story is good. Good, solid characters with consistently strong voices can sell mediocre serial books. Readers read to escape and they have no pity for the authors. They don't know or care that you were forced to draw on painful memories and cry buckets of tears to make the characters true-to-life; they only know if they can identify with them or not. They can't become that particular character or overcome the obstacle, without the true writer's voice bringing the character to life. Bottom line - if they don't laugh or cry, they won't like your story.
So, to find your writers voice, dig through all the animosity, fear, anger, cruelty, humor, joy and heartbreak of everyday living - past, present and perceived. Twist it, exaggerate it, and give it to your characters to work out. Your readers will love it.