Since you have tagged your question with the terms "ambition" and "downfall," a logical point of attack would be the play as a tragedy, with a tragic hero whose actions lead to his own downfall. In this play, it is often argued that Macbeth is the tragic hero and "ambition" is often cited as his tragic flaw, a character trait that leads to his downfall.
There is however, a small problem with your question. Though the introduction of an essay should make clear the general topic -- in this case I am guessing that the topic is discussion of the tragic hero and his downfall as prompted by a tragic flaw -- it must also contain a thesis statement.
And here is where the problem with your question comes in. There is no such thing as an introduction that can be "used for most answers." The introduction's primary purpose is to alert the reader to the thesis statement that the essay will argue. So, your introduction and your conclusion must refer to this thesis statement specifically and cannot be catchall paragraphs.
Again, using your tags as clues for the direction you would like to take, I would suggest that you describe your topic as the tragic hero -- the main character of a tragedy whose actions lead to his own downfall. Of course, then you must create a thesis statement, in which you state which character you intend to argue is the hero of the play and what the flaw of the character is that leads to his/her downfall. As I mentioned above, your tags suggest that the flaw is "ambition."
In creating the essay, again, there is no general way to word a conclusion. Its function is to restate your thesis and provide a final summation of your point of view. I have provided some links below, both in reference to essay structure in general and the topic of the tragic hero.