My top five would probably be…
- Expand your idea.
Pretty self-explanatory, but this stage can include planning or heavy outlining. Basically, the newbie needs to know that once they get their idea, they need to expand on it and then figure out how they can go from point A to point B. I also like to tell people that they need
- Read and research.
This is usually for any part of the writing process, but basically, if they run into a hiccup along the road, they should probably reach out to other writers for help. This can be in the form of writing forums, blogs on Google, or using actual books similar to their genre and target audience to figure out what they may need help on.
- Focus on what you enjoy.
If you want to write a story about a fairy princess who becomes evil, but feel like people won’t read it, still write it. If you want to write a story about a dragon that becomes exiled because they were nice to humans, and feel like people won’t read it, still write it. Write what you want to read. You do have to be ready for rejection because not everyone will like your book. And that’s okay. But it’s also important to think about what you enjoy, not what others enjoy. Especially since there will be people who will enjoy the same things you do.
- Stop trying to make perfection happen.
The first book you write won’t be the greatest, let alone a first draft of any book you write. And that’s okay, because you can improve. You can become a better writer. But don’t dwell on this first draft, this first book and think it needs to look perfect. It won’t happen. Even published books need more improvements. On the opposite end of the spectrum, don’t assume your first draft (or first book) is perfect either. Because I can assure you that it is not. 
- Force yourself.
To finish a book, to create a healthy writing habit, to get anything done, you must force yourself to push through. It’s not easy, but if you want to get a book written, if you want to someday publish a book, if you want to do more than hopping from one idea to the other, if you want to actually do the work instead of playing with vision boards… then you have to force yourself. Otherwise it’ll either take you ages to get it done or it’ll never be done.