There are several directions you can go in this essay. You have so many rhetorical techniques to choose from. I'll give you three that you may want to base your essay around
Attacking the Man - Cassius' spends most of his time trying to persuade Brutus that Caesar needs to be killed for the good of Rome. To do this, he needs to persuade Brutus that Caesar is no better than any of them, so Cassius attacks Caesar's aura of immortality by telling Brutus a story of how one day he and Caesar went for a swim. Suddenly, the waves got rough and Caesar would have drown had Cassius not saved him (Act 1, Scene 2, lines 102-113).
Asking Rhetorical Questions - Cassius often asks Brutus questions that aren't meant to be answered. The questions are worded in a way where the only logical answer makes Caesar looks bad, so when he plants these questions in Brutus' head, he gets him to reallys start thinking about the damage Caesar is causing Rome. Some examples are, "Why should that name (Caesar) be sounded more than yours" (Act I, scene 2, line 144)? "Upon what meat doth this our Caesar feed that he is grown so great (Act I, Scene 2, lines 150-151)? When the questions are worded like this, it sure sounds like Cassius has some strong points.
Committing Misinformation - Probably the most dishonest attempt to persuade Caesar is when Cassius writes letters to Brutus asking him to kill Caesar and signs them with names of citizens of Rome. This is extremely effective because Brutus is left to think the citizens of Rome feel Caesar is detrimental to Rome. It moves Brutus to act because he feels Caesar's death will be for the good of his beloved country.