Write. That is the best advice I can give. There are plenty of sites on the internet that accept story submissions and many post them for free. Find one you like and write for that site. Don't try to write perfect stories. Write stories that readers find interesting. Create a fanbase as well as find your voice. What do you enjoy writing about and how. Do you want to write action? Or are you more into plot driven stories? The best way to hone your craft is well known. Practice.
That's the only real advice I can give. The rest is just being determined to finish the stories you work on and having the passion to publish. But nothing can be accomplished if you don't write.