@dnismsns TBH years of just writing got me to where I am, which still isn't that great, but it's somewhere. I'ma just dump a few thoughts:
Reading a lot and picking up what you like about what you read and trying to put that into your work a bit more helps at the start, and eventually you develop more of your own voice.
Grammar and spelling is important because people struggle to read it if your grammar is too bad.
You've got to find the intersection of what you like to write and what people want to read. If you don't like writing it you won't, and if nobody wants to read it they won't.
It's like any other skill where you just have to practice it. You will improve the longer you do it.
In terms of marketing once you've written, I'm the worst person to ask on that front, I have no idea. Make sure you tag a lot and tag accurately and that should get it where it needs to be for Wattpad. I ask my partner to do my covers and stuff for me since he's got a degree in design, so I cheat there :P
That's all relatively beginner stuff, but it's the important stuff. Having fun while writing is how you keep writing, which is how you improve, which is how you get people to like your work, etc.
Good luck!