Becoming a Full Time Author will require you to
1) Have a decent number of books that are out. The more books you have out, the higher the chance of making a good living as an author
2) Having very high quality and very polished books. You can get by temporarily using 'trends' and 'marketing gimmicks'. However, for sustainted success you need very well written, and highly polished books
3) Creating a loyal readership that buy all/most of the books you release
4) Having direct channels to your loyal readers, so you can tell them when you have a new book, or have a discount on one of your older books
5) Some store/purchase method where you can get 70% to 90% of what readers pay. Apple iBooks offers 70%. Kindle Store offers 70% if you price your book between $2.99 and $9.99
6) Some way to keep marketing costs low. Having your own direct channels is one key factor. Another is to find what marketing channels are good value for money for your books and focusing on those. For one author Facebook Ads will be amazing, while for another author it will be a combination of 4 promotion sites. There is absolutely no 'one size fits all' when it comes to marketing. Also, you cannot spend everything you earn on marketing - marketing costs must be some reasonably low percentage (such as 5% to 20%) of your total revenues
7) Run everything like a business, because it is a business. That means incorporation as a company, hiring a proper, qualified Chartered Accountant, and being very serious about measuring Profit and Loss every month (or at least every quarter). If you are making a living as an author, then you're an entrepreneur/small business and you must behave as such

There are certain things that will get in the way of every author wanting to make a living as an author. By identifying these blocks and working around/over/through them, you greatly increase the probability of making a good living as an author
1) The book stores want to divide and conquer. They want nothing more than for all authors to be struggling/fighting over smaller and smaller pieces of the pie. Control as much of your destiny as you can - any control you hand over to book stores will be used to marginalize you. This is the single biggest block. If you are delusional and think book stores and ebook stores are your friends, then consider that their last 'friends' were the Big Publishers, and now book stores are busy trying to eliminate Big Publishers
Keep as much control of your destiny as possible

2) Have direct channels to your readers. Whether it is via a website or an email list, or via social media, you absolutely must have ways to reach readers without paying a tax to reach them

3) Start building ways you can sell direct to your readers. You can send readers to a book store. However, the book store can kick you out any time, they show other authors' books on your book page, they take a crazy cut, they don't give you any visibility but use your readers and sell them other things. The only way to true success is to start selling DIRECTLY to readers. Why did JK Rowling set up Pottermore website to sell direct to readers? To ensure the author gets control and the largest cut of what the reader is paying

4) Write a lot. The more books you have the more you will sell. Every book leads to your Kingdom of Rome. Have as many books as you can write, while maintaining high quality

5) Master marketing. Yes, you already have to master writing and become decently good at other areas. However, until and unless you master marketing you cannot make a living as an author. Think of yourself as a small business and your books as products. If you cannot market and sell your product, you do not have a business. No one will solve the problem for you. You have to figure it out yourself

6) Focus on your loyal readers. This is frighteningly common common sense - focus completely on the people who are buying your books
There are so many people in the world, that if you do a very very good job of writing for your readers, your reader base will automatically grow
Focus on writing better books, providing more value for money, providing more immersion, and writing exactly what your readers want
The Bird in Hand is worth Ten in the Bush. Do not go chasing things that 'might' work. If you have an area you are doing decently well in, the best path forward is to write better for your existing readers, and write MORE for your existing readers. Your readership will automatically grow as you increase quality of your writing and the quantity of books available

7) Do not give in to Greed or Fear. Greed is the $500 course that says - all the secrets of success - just pay us $500
Fear is the bookstore saying - give us exclusivity or we'll hide your books. Avoid both demons - Fear and Greed
If you write well no store can stop you. If you don't get greedy no one can trap you into thinking there is such a thing as 'overnight' success, or some magic secret
Focus on getting successful SLOW

This is all contrarian to what most online 'courses' will tell you. There is, unfortunately, no easy secret to huge success. The amount of time you would waste chasing 'instant success', is much better spent building REAL success
Get Rich Quick - only the people selling the 'courses' and 'secrets' get rich
Get Rich Slow - it's painful and it takes time. However, your chances of success are very high. This is especially true as most authors in your genre/category will waste all their time and energy chasing 'the secret trick of the month' and not work on their writing skills, or their book portfolio, or their marketing skills