If your question is pertaining to one of the major themes in the play which is joy/love as opposed to sorrow/conflict in Romeo and Juliet, I would begin to construct a thesis statement by choosing a controlling idea. A controlling idea is the slant that the writer is taking on a subject. I would advise you to first look at some evidence from the play that fits into each opposing category, and then write the events or quotations on a graphic organizer. By using this strategy, you may develop ideas that can help you construct a solid, concise, and clear thesis statement. For instance, as an example,a thesis statement that deals with the many forms of love in the play might announce the subject matter and then list three different forms of love found in the play. The listing of these three forms of love serves as a plan of action in the essay.