I think that you have a very strong topic with which to work. There are three things I would keep in mind in writing the compare and contrast of Tony and Romeo.
1) I think you need to identify where there are similar comparisons between both characters- I would not summarize the plot or rehash the story here. Rather, I would focus on several things:
A) How are their situations similar? Examine their friendships, their associations, their feelings/ emotions, what they want, what they want to avoid. Essentially, prior to their love interests, where are both of them in life? As they fall in love, how are their experiences similar? What conflict must both of them face and how do they resolve it? How do both feel after the resolution of this conflict? How do both die? Generally, in what do both believe? How is that similar? In restating these questions as answers from the text, I think you have drawn some very strong connections between Tony and Romeo.
B) How are the characters different? I think you can approach this in a very obvious way. Is the manner in which both of them speak similar? How do both communicate their feelings to the audience? Are the settings similar? What are their "weapons of choice"? What might be different in the way both of them die?
C) The last point I would make is that any good compare/ contrast paper must include evidence. This means that when you make your points on similarities or differences, do not forget to use lines from the texts to support your point of view. For example. if you are talking about the difference in how Tony and Romeo communicate their feelings, don't be afraid to go back to each text and show the differences in communication. If you are talking about how their friendships are similar, do not hesitate to identify with whom Romeo is friends and who Tony befriends. Evidence from the text is the best way to prove a comparison and contrast in a valid manner.