I am often asked by aspiring writers, especially those with some critical success writing short stories or winning contests, "How do I become a full-time writer?". The short answer is, "You don't."
I don't actually mean that too personally. It's usually not that one is not a good enough writer, it's that that career line simply doesn't exist any more. In the 1920s and 1930s, writing fiction for the pulp market could garner one a decent income. Unfortunately, that pulp market, and the pocketbook market that replaced it, are essentially gone. The few fiction magazines that remain still pay the same rates they were paying in 1930, so it is no longer possible to make a living from writing short fiction; and pocketbooks are pretty much down to a few dozen best sellers. When I started my career, there were 42 different publishers to whom I could send an SF manuscript...now we're down to maybe five. Given that everyone else is submitting to the same five editors, the bar for entry has been raised too high for mortals to cross, and the wait times to even have one's manuscript read (given the thousands of manuscripts submitted to the same five markets), this is simply no longer a viable career option.
For example, out of the three hundred or so published writers I know personally, perhaps three make what one would consider a decent middle class living; another 20 or so live by writing, but consequently live extremely humble lifestyles. For example, I recall one woman—the author of about i5 books at that point—who exclaimed to our writer's group, "Now I'll be able to buy tea!" when a royalty check arrived. I don't know about you, but not being able to afford a box of tea for months at a time does not constitute "making a living" in my books.
Most writers I know have day jobs to support themselves and their families. Many work as technical writers, so that they are still practicing their craft, but computer manuals and political speeches are not what they would 'count' as their actual writing. Others have jobs in unrelated careers, such as 'spouse'. (Though one writer told me lately that she would have married anyone prepare to support her writing, so maybe that is a related career after all.)
To which aspiring writers often retort, "Well those guys (pointing to the best seller counter) make a very good living. How do I get to be one of them?"
You don't. Because it is not enough to be a great writer anymore; you have to be outrageously lucky as well. (Or, you know, deal-with-the-devil seems the only plausible explanation for the success of some writers, but that's beyond the scope of the current post.) Unfortunately, pointing to a successful best-selling author these days and asking how to get there is much like pointing to a lottery winner and asking me how to make a living buying lottery tickets. Yeah, there are folks that worked for because somebody has to win, but I think we're all agreed that if one mortgages their house to buy lottery tickets,they're an idiot. One has a better chance playing for the NHL as a career path than making it to the exalted ranks of best selling author, so most career counselors will recommend having a backup plan to even the best aspiring hockey players.
The good news is that becoming a published writer is easier than it has ever been. Getting into the big five is next to impossible without an agent, and getting a respectable agent to take one on is pretty difficult, but it is possible, provided that one's work is both to that standard and commercial. But there are lots of smaller presses around, which can deliver a fair degree of quality and prestige,if not best-seller scale sales. And if one can't find a publisher to take one, one can always self-publish. (If you're going to self-publish, I suggest starting with Kobo Writing Life, which is an author-friendly interface, run by author and book nerd, Mark Lefebvre.) Seeing one's book in print (and digital) is easy--getting anyone to buy it after, not so much.
Bottom-line: if you're in it for the money, you're likely going to be disappointed. If you're in it for the writing, then happy days.