Read "Romeo and Juliet" carefully. Pay attention to the themes, which are the big picture ideas that hold the play together.
Make a character list and general plot outline for "Romeo and Juliet." Think of what adjectives best describe the characters and write these down for each one.
Watch a filmed production of "West Side Story" or read the text. Make a mental note of the big ideas and a character list. Begin thinking about how the two works compare to each other.
Compare the plots first. The stories begin in the same way, with a fight. Both conclude with tragedy. Determine how else the plays are similar, and also how the stories depart from each other.
Compare and contrast the settings. On the surface, the plays couldn't be more different. "Romeo and Juliet" takes place in medieval Italy, while "West Side Story" is set in New York City. Look past the obvious differences and see if there aren't ways in which the stories are similar.
Compare the characters in the stories. Determine which ones are intended to be mirrors of each other. For example, Tony in "West Side Story" and Romeo in "Romeo and Juliet" fulfill the same role as the young man in love.
Notice the characters that seem to be unique to each story and what each contributes. Also, notice how even the characters that are very similar have attributes that make them distinct.
Compare the themes of "Romeo and Juliet" with "West Side Story." Both plays deal with young love and the forces that act against that love. Both deal with loyalty and violence. Determine how each of these stories resolves the main conflict.