According to Ben Yagoda, in this article pver at the Chronicle, style is something that
emerges when writers are comfortable and proficient with their tools. Style is expressed unconsciously, but shaped consciously, in revision. It is a whispering, not a shouting voice; whether readers discern it depends on their familiarity with the writer and their own skill as readers. The writer himself or herself is aware of it; identifying, developing, and shaping it is one of the main pleasures of the craft.
That is to say, it’s not what you get just by following the prescriptions in a book like Strunk & White’s Elements of Style, useful though that is for freshmen composition students, and it’s not the “singing of the tortured soul of the writer whose art and therapy are one,” as so many New-Age Creative-Writing publishers would have us believe (and explain, for a mere thirty bucks a pop). Style is just that something special that develops in the work of good writers, and which is all too rare in most books. It’s voice, attitude, and of course something about the way the sentences, paragraphs, and ideas are put together. But you don’t get there by writing the bones, and you don’t get there by merely following rules set out for you by someone else. It takes just writing and writing and writing more, until it’s as natural to you as speaking; then, you begin to have your own unique voice, and that is the root of having style. Anyway, it’s a pretty good article.