Over the past two decades, I have helped scores of people write to "The End." I've been a ghost, a co-writer, a developmental editor and a book writing coach.
I have come to the conclusion that there are 5 things the successful "new" author needs to write a good book:
1. Something Worth Saying
Recognizing the intrinsic value of what you're writing about motivates you in ways that simply saying "I want to write a book" can never do.
Some of my clients are working on their memoirs. One has written a portion of his father's biography. One long time client is continually looking for ways to make the subject in which he earned his doctorate degree interesting and accessible to the average person. They all strongly believe in the value of what they write. That propels them forward.
2. Simple Sentence
3. Structural Integrity
This is where many authors -- new and not-so-new -- sometimes struggle. It's easy to get in the middle of a project and be distracted by a different project: one that's newer, sexier, flashier, more timely, or more salable.
I know that Sir Terry Pratchett would often have 8 or 10 or more books in various stages of completion at a time. Isaac Asimov could work on multiple books at a time. Maybe one day you can do that too. But let's get the first one done first.
That means no dithering. No stopping and re-starting (once you've done your structure work, there's no need for such things). No chasing after other shiny projects. Just focus on getting This One Done.
5. A Solid Support System
Your family and friends may or may not be a part of your writing support system.
That guy who keeps spamming your Facebook writing group asking for agent recommendations is definitely not part of your book support system.
Your support system includes every one who says, "Let me know when it comes out and I'll buy it."
It's every person who hears you are writing a book who doesn't start telling you about this kid they know who wrote a book and got an agent and sold a bazillion copies without even trying.
It's every person who learns you are writing a book and who doesn't remind you that you once failed English class and had to repeat it.
It's your book writing coach. It may also be your neighbor, your co-worker, the girl you talk to at the gym, the family you meet at the dog park, or your dentist.
Tell people you're writing a book. When they ask what it's about, tell them your simple sentence. Look for those people who light up when they hear it, who want to hear more. They exist. Their interest will support you as your write your book. Because -- like you -- they can't wait to read it!