I've struggled with the concept of voice in my writing. It is a simpler concept than I'd originally thought, but polishing it will take just as much effort as I'd feared.
Here's one example:
"Hans Huberman sat sleepy-eyed on the bed and Liesel would cry into his sleeves and breathe him in. Every morning, just after two o'clock, she fell asleep again to the smell of him. It was a mixture of dead cigarettes, decades of paint, and human skin. At first, she sucked it all in, then breathed it, until she drifted back down. Each morning, he was a few feet away from her, crumpled, almost halved, in the chair. He never used the other bed. Liesel would climb out and cautiously kiss his cheek and he would wake up and smile." (from The Book Thief, page 37)
In essence, this paragraph is saying, "After her brother's death, Liesel often woke up with nightmares, and her foster father would come in and comfort her." But when Liesel wrote about her nightmares years later, she remembered the smell of her foster father more than any other thing, so that's what she wrote about. Her brother's empty bed also becomes a symbol that is referred to frequently throughout the whole story.
Contrast that to the book I am reading right now. I'm not far into it, but here is an excerpt. Can you guess who wrote it?
"Miss Maria's name was never spoken of at M_____. Her father had utterly forbidden it. A man of high principle and strong moral judgment, he had suffered anguish unspeakable at the time of his daughter's degradation...and could not bear the least allusion to any topic bordering on reference to his abandoned daughter.
"Lady Bertram was not so nice. Never, even when they were small, having been deeply attached to her children, she felt much less interest in them as they grew older, and had long ago divested herself of any anxieties or gratification regarding them, unless in a matter directly concerning herself...That Lady Bertram never alluded to the erring Maria was due primarily to a complete lack of interest in her disgraced daughter's fortunes; in fact, she was hardly remembered from one year's end to another."
Would you have guessed Jane Austen? I would have. But this is from Mansfield Revisited by Joan Aiken, who wrote it as the sequel to Mansfield Park by Jane Austen. (The excerpt quoted above is from Mansfield Revisited, pages 17-18).
I looked everywhere for a definition of voice that I really liked, and I never found one, so I'm taking everything I have learned and making up my own.
1. Voice is all the choices you make as a writer that convey your attitude, your personality, and your values to the reader.
2. The speech and thought patterns of your main character or narrator, and, to a lesser degree, other characters in your story.
When I first started writing young adult fiction, and I read that publishers were looking for a strong voice, I thought they were referring exclusively to the second definition. More specifically, I thought they wanted a really snarky narrator, like Alcatraz Smedry:
"I've been many things in my life. Student. Spy. Sacrifice. Potted plant. However, at this point, I'm something completely different from all of those--something more frightening than any of them.
"I'm a writer.
"You may have noticed that I began my story with a quick, snappy scene of danger and tension--but then quickly moved on to a more boring discussion of my childhood. Well, that's because I wanted to prove something to you: that I am not a nice person." (Alcatraz and the Evil Librarians, by Brandon Sanderson, page 14. You can find my review of this series here. )
In case anyone else was suffering from the same delusion I was: voice does not equal snarkiness.
Voice is the tone of your story, your choice of theme, your choice of audience, the topic you pick, the details you include, the personality of your characters, even the types of words you pick and the length of your sentences.
Voice might be conveyed with ellipses or italics, but probably not. When you choose to break any particular writing rule, that becomes a part of your voice. So does following the rules closely. In The Knife of Never Letting Go, voice is almost like a picture on the page, with handwritten sentences, in a variety of styles, written on top of each other until meaning is almost indecipherable. The author does this to convey a sense of CHAOS.
In the Book Thief, the author's voice includes poetic phrases like "she sucked it all in, then breathed it until she drifted back down." He uses senses to evoke a feeling of MEMORY.
With Jane Austen, part of her voice includes explaining the motivations behind people's actions with a dry wit. When she's finished, we understand her sharp conclusions about people without her having ever actually cast judgment. It is obvious that Aiken has put considerable effort into figuring out Austen's voice so she can imitate it, and she does an admirable job. However, I think Jane Austen used character sketches to help us draw conclusions about SOCIETY and MORALITY, and that is one way that Aiken falls short.
All of Brandon Sanderson's considerable talent is used in Alcatraz to draw our attention to ABSURDITY and PARADOX. The story line behind the Alcatraz books is full of holes, purposely dug by the author himself. But Alcatraz becomes a hero teenagers can relate to because he is likeable in spite of feeling unlikeable. He learns that his weaknesses can transform into his strengths.
If you are interested in honing your own voice, this is the best advice about finding your voice that I've seen on the internet.