About to release the fifteenth book in her popular Bad Hair Day Mystery series, author Nancy J. Cohen knows a thing or two about how to write a successful book series. The two key ingredients, she says, are a likeable main character and a fresh plot with each book. Most importantly, you want your readers to care about your protagonist. To create this relationship, you must develop a character that shows growth and embarks on an inner journey that your readers want to follow. To keep each book fresh, Cohen recommends bringing in new secondary characters or changing the setting. She cautions writers to use these techniques carefully, as readers like to come back to the familiar places and recurrent characters they've grown to love. Cohen keeps the series fresh for herself by learning and writing about issues or topics relevant to Florida, where her cozy mystery novels take place.