You want to study a soliloquy, either Romeo in Aft Two scene Two or Juliet In Act four secen three are the best ones. Make sure you can quote from them, and know how the character is feeling while he/she speaks.
Also want to prepare a key scene in the play. I would pick act 3 scene one because of all the action in it and how it advances the plot of Romeo's banishment and tybalt dying effects Juliets marriage to Paris.
Hope this helps a little.