1) Pantser or Plotter?
Writers will ask whether you are a pantser or plotter. A pantser writes by the seat of his or her pants. Page one, blank screen - GO! A plotter creates an outline of the story before beginning. Many writers fall somewhere in between, doing some outlining, but not hesitating to depart from the outline if the story veers in a new direction. Which are you? It may take years of writing to decide. You may also discover that being a pantser works better for one story, while careful plotting is required for another. Experiment.
2) Don't hurry.
There may be anecdotes about people writing a best seller or classic in a weekend, or a matter of mere weeks. Good luck with that. My best work has taken time. Due to deadlines, that time is often compressed, but the work will not be cheated of the hours.
On that same note, don't rush to get your work before agents, or push it prematurely into self publication. After you have written "the end," set your story aside. Days, a week or two, even a month will allow you a fresh perspective.
3) Don't quit the day job.
When I first became published, I joked that I'd be able to earn my living from writing on the day I retired. Sadly, this is probably going to be the truth. The economic reality of writing is harsh. Short story author R. T. Lawton has quite a bit to say on this topic in his article: https://www.sleuthsayers.org/2017/03/while-were-at-it.html
I'm not saying it can't be done, but the majority of folks I know who are writing full time are retired, or are supported by a spouse. Be cautious before you leave that paying gig. A steady paycheck, health insurance, pension, and paid vacation are non-existent for the self-employed writer.
4) Learn the business.
As budding authors, we crave learning the art and craft of writing, but the business end? Not so much. How can you learn, besides reading books or blogs? Join a writing group attended by successful authors. By joining the Mystery Writers of America, I was fortunate to meet published authors who freely shared their experiences at local chapter meetings. Libraries may offer writing workshops, or can direct you to local writers' groups. If you attend a conference, include sessions on the business aspects of writing.
I'm not talking strictly about the financial side of business, although learning the best method to track your income and expenses is important at tax time. You will need to know how to write a synopsis. (Hint - you can't do much better than Pam McCutcheon's how-to book.) Where to find agents representing your style of fiction. What is the proper etiquette when pitching to an editor at a conference. If you want a career writing, treat it like any other business, and educate yourself.
5) Renew the joy.
Writers can burn out, just as in any profession. I have heard complaints from the entire spectrum of writers, whether unpublished or multi-published. At some point, it becomes a job. Maybe even drudgery. You begin to hate your story, dread sitting in front of the computer, and doubt your sanity for thinking you had the talent to write fiction. Before you throw in the towel, ask yourself these questions.
Who is stopping you? A negative person in your life? Someone who needs your attention, whether a child, a boss, or an elderly parent? Yourself? Can you turn the negativity into motivation? "I'll show them - I am a writer!" Find a way to balance the needs of people in your life with your own goals. If you're not happy and healthy, how can you be a good parent, spouse, employee, caretaker?
Why did you begin writing in the first place? A book inspired you? Did you escape pain through reading, and want to give someone else that gift? Do you have fond memories of being read to, or reading in a favorite comfy place? Revisit your earliest motivation to be a writer.
What did you have to say that was so important, you were willing to sacrifice other aspects of your life in order to hammer out words for hours on end? Is that message still valid? Your message, or theme, doesn't have to be lofty. Distracting readers from their worries and problems with an entertaining story can be more valuable than any deep literary tome.
That moment will return when suddenly the words flow. The scenes click together. The characters jump off the page. You become lost in your own story. You remember the joy of writing, and why you started on this crazy journey.
You can do this. Even if you have to write in snatches of stolen time. Even if you have to battle doubts, whether from people around you, or yourself. A good deal of success in writing is mere persistence. That is a trait we can all nurture.
You can find the Mystery Thriller Week group on Facebook.