If my 19-year-old self were across the table, asking for advice on how to stay sane through four decades of devotion to the ideal of being a writer, these are a few of the hints I'd pass along.
Discover your strengths so you can put them to best use, and your weaknesses so you can work on them. Start by figuring out if impressions come to you more readily through the eyes or ears. This is important information to have. Also, develop assertiveness. Just because you work at home, it doesn't mean you are interruptible at any time, for any trifling reason. Learn half a dozen ways to impress this concept on others.
Self-confidence is admirable; arrogance is not. An artist who asks, "Is this material good enough for me?" harbors a counterproductive attitude. All material is good. The question should be, "Am I good enough for the material?" Occasionally some little fact, a paragraph in a newspaper, or an overheard remark will make you say "Huh?" or "Hmmm..." Save every one of those seeds, for the times when you wonder what to write about next. Just about anything that provokes the "Huh?" reflex or the "Hmmm…" reflex will turn out to be worth your while.
A first draft isn't what you want to turn in - certainly not to an editor, and even less so if you're self-publishing and there's no trace of a gatekeeper between you and your public. When people give you their attention, to present them with a first draft is actually kind of rude. There's no piece of writing that can't be improved. The first go is the let-it-all-hang-out round, where you can be ornery, repetitious, sloppy, unstructured, digressive, and whatever else it takes, to get the ideas down with no editing or self-censorship of any kind. But then go back for at least one more pass, and turn that undisciplined rant into a polished object. You owe it to your readers; but even more, you owe it to yourself.
Writing stuff that's hard to understand doesn't show how deep you are. Enough people will find your work incomprehensible anyway; there's no call to make it worse. Don't engage in what Somerset Maugham called "willful obscurity." Conversely, never write down to your audience. If you're working in a genre that requires you to condescend, then it's just another job. You might as well be picking cotton. Consider becoming an office machine repair technician instead. It pays better.
If you start on a piece of work with the goal of sending a message, it'll probably end up being lousy, plus nobody will get the message. If you start out aiming for the truth, there's a much better chance of emerging with a good piece of work, and at least a slim chance that somebody will get the message. This is not to say you should only write non-fiction. The work of fiction is the most powerful mechanism ever invented for packaging the truth.
Maintaining a diary is a good way to keep yourself honest. Check back later, read about the events and emotions of the past, and see how adroitly your mind has managed to twist things around in the interim. It's a sobering lesson. Solid work habits are good, and realizing when they need to be broken is even better. Don't be afraid to go off the deep end, but don't adopt crisis as a lifestyle. Go ahead and be the wild-eyed Artiste, but cultivate a secret identity: the competent professional who can deliver the goods. Along with writing, pick up at least one other skill. This way, you can always tell yourself, "I'm a better writer than any quilter I know, and a better quilter than any writer I know." At some point, this will save you.
There are plenty more caveats that could be offered to my 19-year-old self, but even at that young age, I think she had already discovered the most important one: When faced with any decision, the first thing to ask is "Will this be good or bad for my art?"