Two Powerful Words: What If?
The words "what if" are among the most powerful words a writer can have in his or her vocabulary. What if this story were set in a different era? What if this story were a different genre? What if the main character is the opposite sex? What if this story is set in a totally different environment? The list can go on and on. There are many ingredients to play with. Try them all out!
When thinking about your premise, if you get stuck, just start asking some "what if" questions. What if the ending is really the beginning? What if a different audience might be better for this book? What if the chapters are organized in a unique way? What if a different title lent itself to a shift in the tone of the whole story idea? What if this story is told through the lens of a different theme?
Give yourself full license to ask What If of your story - or even a character, or a scene - and see what comes to mind. You might be very surprised.