Start by examining the basic formula for your story. Let’s play with the “Secret Baby” theme. Everyone knows the premise is a couple who have come together for the sake of a child. This is such a popular theme for category that, to be honest, I’m not sure there is any way to create a slant that hasn't already been done but we can certainly add some twists.
We'll start with Heroine who hasn’t seen her Hero in five years. Let’s say they parted when he was deployed overseas. Now we’re blending something relevant to give it a new twist. But that’s not enough. He is injured during battle and sustains some facial or bodily disfigurement. He can’t bear to let her see him like that. Alone and bitter, he breaks it off with her.
What just happened? We introduced a second theme – Beauty and the Beast. The Heroine is devastated but goes on with her life. Realizing she can never love another man like she loves Hero, she adopts a child to raise. And let’s say the child is of Afghan descent, the very place where Hero has been stationed.
The scenarios for conflict here are limitless when and how they reunite. Or substitute Vampires and Werewolves. Or let the Hero come home with a child – possibly his or one he rescued. How about adding a marriage of convenience theme? It’s been done many times but how could you make it different? How can you make this tried and true theme "yours"?
Crafting a “new” story out of an old formula is truly about developing characters so real the reader doesn’t think about the formula but rather what’s happening to the hero/heroine. The more angst they suffer, the easier it is to draw the reader in emotionally. Keep your novels fresh by writing compelling tales and adding a colorful secondary character.
We’ve all read books that were so predictable we literally flipped through pages due to gradually losing interest. Surprise the reader with unexpected plot twists. Keep your writing razor sharp. No lag time or excessive descriptive passages.
Your voice should be unique but not bizarre. The reader still has to understand what's happening so try to keep it realistic. The best paranormal and fantasy stories are abnormal creatures with humanistic emotions and reactions. I personally believe that's what keeps Twilight so popular. It's truly a story about young teen love. Bella just happens to have two suiters who have unusual heritage. Their emotions are human, however.
It wasn't so long ago Amish Romance was considered boring, especially with erotica hot and heavy in the market. Then several writers developed characters and plots so captivating that readers were hooked. Think back ten years ago. We were all reading multi-volume family sagas. Now it's paranormal.
Remember, there’s nothing new under the sun. You just want your reader to “think” there is and that requires smart, savvy writing.