You should always write in the style that is most natural to you. It may well be different from your speaking voice but should always reflect the way your mind works.Another thing Mr. Parnell writes is:
Secondly, your voice doesn't have to be 'original'. You can waste years of your time wondering what 'originality' is and trying to define and acquire it."Voice" is one of those things that is difficult to pin down for a writer, but this article explains it well and gives some methods that a writer can use to discover his or her own voice.
When critics, publishers and agents say they want 'originality', I believe they have no idea what they mean. They merely confuse writers by demanding something so nebulous and indefinable. I think what they should really be asking for is 'honesty'.
The simple truth is you already possess all the originality you need. You are already unique. No-one else thinks and writes like you do - trying to undo your own originality by constantly striving to be anything less than yourself is counter productive. Trust yourself.
Another very useful article at Fiction Factor is "Editing Fiction" by Lee Masterson and Tina Morgan. It goes beyond looking for typos and grammar mistakes and gives you a list of questions to ask yourself about your piece of writing in an effort to make it much more interesting and readable. The questions cover plot, pacing, setting, characterization, dialogue, and point of view. Very helpful, I think.
An entire set of articles at Fiction Factor is on world building. If you are planning a novel set in an imaginary world (usually fantasy and science fiction, but you may find other uses for this information--perhaps in a poetry cycle or an epic poem), these articles should help you create a complete world for your characters to inhabit. Creating a consistent and believable (in the context of your story) world isn't the easiest thing to do, but it will make your story much better if you plan ahead.