OK, first off I'm either the best or worst person to give you advise.
I belong to the
Harlan Ellison "Pay the F***ing Writer" School of Writing. I feel that too many amateurs give away their writing, which makes it hard on professionals who take the job seriously. While I do give away some of my stories for free, most of what I write is for sale. Self-publishing ebooks is easy to do and there's no reason not to these days once you feel confident enough to do it. (It took me 25 years of writing.)
First: Read. A lot. Everything. Things you never would normally read. Fiction and non-fiction. I grew up on science fiction and these days one of my favorite genres is romance. In my writing one of my favorite characters in an urban fantasy story was inspired by, among other things, a novel and character named Fay by Larry Brown, which is about a teenage runaway in 1980s Georgia. I spent a year researching Byzantine Constantinople, Zoroastrianism and prostitution in the Roman Empire for a novel. I love non-fiction about Transhumanism, string theory, cosmology and memoirs by porn stars and truck drivers. Seriously, reading anything and everything can help your writing. And don't fall into the trap of "I don't read my genre so I won't steal ideas" because of a reason I'll explain below.
Second: Write until your fingertips fall off. Ideally, start a writing habit like saying "200 lousy stinking words a day." Like reading, write about everything. Even if it never leaves your hard drive or notepad. Also, I don't do that because I'm lazy.
Third: Dream journal, some of my best ideas I literally dreamed up.
Fourth: Read books on how to write. They help immensely. I could make recommendations, but I won't other than to say Writer's Digest has a nice series of books. I have a formal education in writing and found it immensely helpful, but I don't view it as a requirement.
Five: Ideas are a dime a dozen and a nickel on Tuesdays, and most people want to make their own anyway. Ideas are cheap, don't think everyone's trying to steal them; they don't want them and even if they take one it won't be what you thought of anyway. In 1991 Neil Gaiman put out a comic book about an orphan boy wizard named Tim Hunter who was drawn with round glasses being contacted for his schooling via carrier owl, and it's mostly forgotten. Six years later an unknown writer has a virtually identical idea, except she called the boy Harry Potter and at one point she was a billionaire. Besides that, their stories are nothing alike.
Six: Accept constructive criticism, grow a skin against haters. I joined a writer's club almost 20 years ago, went intermittently until recently and found them both amazingly useful and a total waste of time. Broadly speaking, they gave wonderful advice, but repeated the same thing too often, but the club was so cliquish I ended up leaving. A good club can be wonderful, a bad one has you leaving hating every word you've ever written. Don't stay in a bad one, but don't ignore sound criticism.