The posters here are absolutely right, the first thing you should do is look to an alternative income source. Making money from novel writing is a long-term goal and takes decades, not months or years and if you are relying on it for income, it will put you under incredible strain to succeed. Writing should be a joy, not a chore, don't do that to yourself.
Next, start with your basic English writing skills, your local university should have English 101 courses that will improve your grammar, punctuation, spelling and sentence construction. I'm a native English speaker but I still took this course before starting my writing career.
Personally, I would recommend a creative writing degree if you're able to afford it/can find a good one locally. There is a lot of debate over whether creative writing can be taught in this way, and whilst I have learned far more from actually writing, it did enable me to study the classics and gave me a good grounding in story construction. MOST IMPORTANTLY though, a good creative writing degree will teach you how to critique your own and other people's work and this is an essential skill. You will also meet other writers and a support network is vital on this journey.
Devour books on writing. I would start by reading the following books:
"On Writing" by Stephen King
"Stein on Writing" by Sol Stein
"Writing a Novel and Getting Published For Dummies" by George Green and Lizzy Kremer
"Word by Word" / "Bird by Bird" (the audio seminar) by Anne Lammott
"Writing Down The Bones" by Natalie Goldberg (audio version is great)
These books will give you a feel for what it takes to be a professional writer.
WRITE WRITE WRITE nothing teaches you to write like writing does. Write like your life depends on it and get it out there. Submit to online critique groups, send it out to magazines, get your work torn to pieces, get rejected, learn to take feedback on board and then write again.
Finally, to give you an idea of what you're up against, let me share my personal story/timeline with you:
After quitting a well-paid job in I.T., I spent 4 years studying creative writing at three universities around the world and read voraciously on the craft. I spent three years writing my first novel and made mistakes with it I couldn't foresee despite years of study. It got rejected. I spent a year re-writing it and it still got rejected. It now sits under my bed. I spent another year writing my second novel which, having learned from my mistakes, I was lucky to secure agency representation for. We have spent a year in re-writes and are finally submitting to publishers next month.
It has taken me a decade to get to this point and publishers will take approx 18 months to get my novel out. Or, I could still get rejected. My story is not uncommon. The majority of successful writers out there have several published books before they find success (let alone the unpublished ones under their beds). Wiki any successful author you know and see how many books they published before succeeding with a breakout novel.
Finally, read this, so you understand the realities of traditional publishing and consider whether self-publishing is for you:
If this is a dream for you, don't give up. It's by far the most rewarding (though often painful) thing I've done with my life. But start this journey with your eyes wide open and plan for the long game.
Best of luck to you.