No author creates their book completely alone. At the very least, you need an editor and help creating your book cover before you even think about publishing your work. While this is the era of self-publishing, learning to do every task needed takes up valuable time you could use to write your next book. When it comes to deciding how to use your time, it only makes sense to do what brings in the most return. For everything else, it's better financial policy to hire an expert, someone who does each task as a full time job. Not only will it get done in a fraction of the time, because there won't be any learning curve, you'll end up with a better product because of the professional input.
Plot Doctors
You know about your characters and what happens in your story, but you're having a hard time getting from the beginning to the end. What happens in the middle? When should the dead body show up? How do he and she meet and fall in love?
Every well-written story follows a pattern, one that's been used since people told stories around campfires. You can read about the three-act plot, the five-act plot and the snowflake method, and you might still be lost when it comes to outlining your novel. This is where a plot doctor comes in. They don't write your story; they just create a roadmap that allows you to take the necessary steps to get your characters where they should be going.
Blurb Writers
Your book description, or blurb, is the second most important piece of marketing you have behind your book cover itself. If the cover draws strangers in to look, your blurb convinces them that they want to read your book. Writing book blurbs is a science, and one you can learn to do well with a bit of studying. On the other hand, why not hire someone who's already learn how to do it, and spend that time working on your next book in the series? For something this important, you need the best you can get.
Beta Readers
While many authors use friends and family members as beta readers, doesn't it make sense to have an unbiased opinion for this first critical view of your book? Beta readers aren't editors, they read your first or second draft to see if the story's going where it should be. They find plot holes, let you know if a character's changing attitude halfway through the sixth chapter, and lets you know if the American tourist is using strictly British slang terms. Think in terms of broad strokes. A beta reader will put you back on target, often before you've gotten even halfway through writing the book.
Social Media Expert
Whether you are self publishing or are going the traditional route, you're expected to shoulder the burden of book marketing and social media. Even with the slickest technology and strictest scheduling, this can take up an enormous amount of your time if done right. A virtual assistant/social media expert can post on your behalf and keep track of your Facebook pages, your street team, and even your Pinterest boards, leaving you time to concentrate on what's really important.
Keep the Faith and May the Force be with You!