Firstly, please be sure to read everything on this page - https://review0.com/author/authors-start-here/pages/path-7-i-want-to-be-a-full-time-author-and-make-a-good-living.php
Everything written on that page applies. Before making a 'very good living' you should focus on ensuring you make 'a good living'

The rest of this page will cover MASTERY and the areas in which you have to gain mastery (one or more). Fundamentally, you need two things
A) MASTERY of one or more of the Critical Areas for Authors
B) As much Control of Your Destiny as possible

Books is very different from other professions. In most professions, if you become one of the best in the world you are guaranteed to make very good money. In Books, you have to attain mastery in additional areas such as marketing and becoming self-reliant and selling yourself. Additionally, in Books, there are many 'middlemen' who will gladly steal all the 'value' you are creating and give you almost nothing

First, let's look at the areas you have to master. If you attain Very High Level Mastery in one of these (i.e. one of the very best in the world), or High Level Mastery in multiple areas (i.e. one of the top 1000 in the world in multiple skill sets), then you will sell a lot of books

If you want to make a very good living from books, there are no two ways about it. You must become one of the best writers in the world, and also gain mastery in one or more areas like marketing, self-reliance, selling yourself, virality, word of mouth marketing, etc
Note: After discussing this, we will look at Control of Your Destiny i.e. ensuring that when your books sell, you get a decent cut. First, let's look at mastery

Areas to Master - Very High Level Mastery (i.e. Becoming One of the Very Best in the World (Top 100)) in any one of these areas will almost certainly guarantee you a very good living as an author
If you cannot attain that, then High Level Mastery (i.e. one of the Top 1000 in the world) in two or more areas will most likely get you a very good living as an author

1) Writing really really really well
2) Writing very compelling stories. Where the stories enrapture and capture the readers
3) Writing what there is huge demand for, and where demand is not satisfied by authors
4) Marketing i.e. awareness
5) Selling Yourself i.e. creating a very good story ABOUT YOURSELF and selling your books based on who you are. It is not just Biographies & Memoirs where this can be leverated. You can use this in any genre/category
6) Self- Reliance i.e. direct channels to your readers and they can buy straight from you. If you can get 80% of what readers pay, while having very low marketing costs, you can make a very good living even without reaching very high number of sales
7) Writing for TV and Movies. TV Studios and Movie Studios and Actors and Scriptwriters are always looking for 'a great story'. Just remember to get a top notch legal expert when signing any contracts
8) Excellent Polish and Finish. You can sell a lot of books based just on polish and finish. A survey (perhaps as unreliable as surveys are wont to be) found that only 10% of people who bought a book read beyond the first chapter. If you polish your book enough and market it right, it doesn't even have to be well written
9) Word of Mouth. If you figure out a hook or story that makes readers share your book with other readers, then you can let them do the marketing for you. This can be something subtle like a very unsettling book that they feel they must share. It can be something overt like tapping into some common fear or interest people currently have
10) There are several other skillsets that by themself can make you a huge success. We've listed 9 above. Perhaps we'll cover some of the other ones later. Each of these deserves a dedicated page (perhaps later)

If you thought mastering one of the above was tough, now you get to the really tough part i.e. Taking Control of Your Destiny
You work very hard and write a book. You polish it. You do the marketing. You build your readership
Yet, you are completely at the mercy of the book stores
Why? Because they control the Purchase Point for your book. They control the book store and can choose what to show and what not to show

That brings us to the Key Problem in being an Author - The middlemen in between you, the author, and your readers, can extract as much tax as they want
Before Apple came into the market and started offering a 70% cut, Amazon Kindle store gave authors only 35%
Many Publisher deals in the past (and some now) give authors only 8.5%

On the other hand, if you can create a direct selling channel to readers, which you control yourself, you can get 70% to 97%

It's almost impossible to do all this yourself, so you have to do the next best thing i.e.
A) Create a strong enough reader base such that you can get reasonable terms from book stores and/or Publishers
B) Create direct sales channels, so you can sell directly to at least some portion of your readers. And keep increasing the percentage of direct sales

Remember, in the end the game is going to be won or lost based on how much Control You Have Over Your Destiny. Everything else is details