For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I:
Faustus considers and rejects various academic disciplines. Theology? Nope. Medicine? Pssh. Law? Hardly. Magic? Hey, now there's an idea. But every awesome magician needs a faithful servant, so to gain the services of Mephistopheles for twenty-four years, he signs over his soul to the devil.
Act II:
Mephistopheles and Faustus debate about hell and the devil and discuss astronomy—everyone's favorite topics for dinner conversation. Faustus travels among the stars and planets and around the globe before landing in Rome to make trouble for the Pope. Later, Faustus does magic tricks for the Holy Roman Emperor and the Duke and Duchess of Vanholt, humiliates a courtier, and cheats a few peasants. Basically, the middle of the play is all about Dr. F's fantastic exploits, now that he's got a demon doing his dirty work.
Act III:
Faustus's life is coming to an end. After admitting his pact with the devil to the Scholars, who resolve to pray for his soul, Faustus retires to his study to await death-by-demon-demolition. As Faustus begs the powers that be to make his soul disappear rather than suffer, his devils arrive to take him to hell. The next day, the Scholars find Faustus's body torn to pieces. Well, that's what happens when you sign over your soul to Lucifer. Sorry, buddy.