There are many ways to take a critical pass at your writing to tighten up your narrative and make it more enjoyable for your reader. Asking yourself "Why do I need this in my story?" from a macro to micro level, is one approach.
Life is short. Life is busy. How can you possibly add writing that book you to your stacked schedule? It starts with a commitment. To finish writing a book, you need to get started.
Do a slow read of your writing. Have you chosen your words well? Is your mind jumping ahead because the text is perfected or because you could cut it and lose nothing? If you don't want to read those words, will anyone else?
Open a book you love to a random page and read one sentence. Can you hear the author's voice? Does it evoke an emotion? Does it draw you in? Now open your own work. How does it fare?
Whether you are working on draft material or devising a story in your mind, one element of great writing is cranking up the extraordinary to pack in information, meaning, and creativity.