Some say that every story has been written before. There are no original stories, they say. Well then, is your story even worth telling?
Of course it is! Unless we become clones eating "soylent green", there will always be opportunities to create unique stories.
Ask one hundred writers to tell the Dickens' story, "A Christmas Carol" and you will get one hundred different stories. (There might even be some paranormal romances in there.) How can this be? If you're starting with the same theme, the same plot, and the same characters, can it still be original?
Sure it can. Take some inspiration from the Rubik's puzzles above. These are just a few variations of the Rubik's Cube. There is something familiar about each of them. It's because they are really not too different from the original design. Tweak something minor and it's easy to see how dramatically unique each one can be.
What can you do to make your story unique?
Like the cube, twist some familiar aspect of a good story. For example, look at the Creation Story. The first person on Earth was lonely until a companion was created for him and together they populated the planet. T.C. Boyle also wrote a great story about companionship and populating the World. It was called, "After the Plague". In his story, the narrator thought he and a female companion were among the last people to survive on Earth...but they hated each other. That twist makes for good reading!
Even if you start with an old premise, you can create an original story. Your personal experiences and world view will guide you. Your voice alone, can be enough to turn an old, cliché of a story into something new and fresh. If anyone has ever mused to you in conversation, "Interesting point, I never thought of that," then you have what it takes to write original fiction.