The best investment I’ve ever made was to hire a developmental editor. A developmental editor is very different from a copyeditor. A developmental editor looks at the bigger issues of your manuscript. She inspects if you follow the correct structure, if your characters are well-developed, POV, dialogue, voice, pacing and plot. It’s very difficult to be objective with your own story and a developmental editor will dissect your novel and see what works. A developmental editor can bring your novel within publishing standards and it's important to find one with good credentials. I've made the habit of hiring an editor for all my books.