Set aside specific time for writing. Even if it's just 30 minutes a day. Start with a simple idea or character and build the story around it. Try different genres to keep things interesting. For example, you could write a mystery short story one day and a science - fiction one the next.
Join a writing group or workshop. There, you can get feedback on your stories and learn from others. Also, practice writing different types of endings, like a twist ending or a happy ending. Don't be afraid to rewrite and edit your stories multiple times to make them better.