What is the best way to revise (review for) an exam on Romeo and Juliet?
In reference to some intense and general study skills, the best way to review for an exam on this wonderful play by Shakespeare is to read the notes that your teacher has given you. In fact, read them again and again. If your teacher hasn't given any notes on Romeo and Juliet (expecting you to read the play all on your own), which is highly improbable, then the best thing to do would be to review the summary, themes and characters of the play on this very website: eNotes.
ENotes is an absolutley wonderful way for you to prepare! Simply look at the right hand side of this very web page and click on some of the "Popular Links." Perhaps you could even explore the Romeo and Juliet discussion page by clicking at the tab lableled "Discussion Board" right above your question.
Finally, and I realize it's kind of crazy for an English teacher to suggest this, . . . I would suggest watching more than one version of the movie. Romeo and Juliet has now been directed by an incredible number of talented directors and acted by an incredible number of talented actors. It has always helped me remember the nuances of the play by grasping a good visual image that you may or may not have been able to do by simply reading the play.
As an end note, I have to say that you shouldn't neglect studying the life of Shakespeare in preparation for your exam. Often times teachers will include quite a few questions on Shakespeare to show that you understand the play's very famous author.
Good luck to you!