Introductions are often the most difficult part of writing an essay, and sometimes it is easier to write the rest of the paper before writing the introduction. In any case, the purpose of an introduction is to capture interest and prepare your readers for what you are going to say in the rest of the essay.
For an essay on The Crucible, you undoubtedly have a specific focus which you will be writing about, and that is a good place to start thinking about your introduction. For example, if you are writing about how pride affects the outcome of these trials, a quote by or reference to Danforth at the end of the play when he refuses to even consider a pardon for Proctor and the others might be useful:
I will not receive a single plea for pardon or postponement. Them that will not confess will hang.... Postponement now speaks a floundering on my part; reprieve or pardon must cast doubt upon the guilt of them that died...
(The entire section contains 494 words.)