One important element of writing a book is your style.  Hopefully your own style comes naturally to you and you don’t have to think about it.  You must learn to recognize when you’re writing with you own style and when you’re trying to be someone else.  This can be difficult.  If your story is inspired by, say The Chronicles of Narnia, you may find yourself trying to write like C.S. Lewis.  This almost certainly leads to awkwardness in your sentences, and more often than not is really annoying.  It’s also important to realize that sometimes the kind of style you like and your style are two different things.  No matter how bad you want to mimic another style, you must stick to your own, especially since mid-way you’ll probably drift back to your own style and the two won’t mix well.