The Book of Luke by Jenny O'Connell

Emily Abbott is known as a nice girl at her high school. When she moves back to her old hometown, Boston, during her senior year, she is able to reinvent herself. She rekindles the friendship between her old friends Josie and Lucy, who don't know what to put in the senior time capsule. Their idea arrives in the form of Emily's return: they're going to create a reference guide for guys to treat girls the right way. Emily soon finds herself trying to capture the affection of Luke Preston, the most popular guy in school.