First, craft each character with his/her own GMC (goal, motivation, and conflict). Even the secondary roles. Sometimes exploring the story from the eyes of one of these less-important characters will open new avenues and conflicts for the hero and heroine.
Second, be conscious of the many types of heroes there are and what makes us “bond” with them. Here, I’m reminded of the TV show Heroes. The characters all had super powers and were all flawed in some way. Some were villains, others good, and a few were underdogs. To be emotionally invested in each character, the writers gave them each something for the viewers to connect with emotionally or be a person one would want to be. My favorite type of hero is the antihero. This is a hero who lacks morals or virtues and is driven by self-interests. I always connect with a good story with an antihero making a character arc from bad to good.
In Heroes, this was most evident in the character Sylar, who murdered people recklessly and selfishly, but could almost be forgiven since he longed to stop killing. I was in emotional turmoil when the show’s writers aired an episode with a flash forward where this most-hated character had a child, whom he obviously loved and cared for. I was confused and bewildered, but yes, I eventually changed my mind and connected with Sylar–even after everything he’d done in the past. Maybe I wouldn’t enjoy reading a romance with an antihero as dark as Sylar, but he’s certainly interesting.
Do you have a favorite hero type?