Outwardly, Iago seems honest but he is actually a very petty and small person. His main ploy is playing on other people's insecurities. His interactions with Othello are a prime example. Othello is an honest and virtuous man but has the flaw of jealousy. Iago's tone and persona is of a very honest and respectable man. In this way he is able to lure Othello into his trap. The first half of the play is very much Iago's. Most of the action is seen through his point-of-view. It is important to note that the audience sees a side of Iago that the other characters don't. Namely that he is scheming their destruction. In this way, his "honest" persona is clearly ironic. It is a ploy which he uses to his advantage. At the end of the play he reveals that he destroys because he destroys because he can't stand that Cassio "will have beauty in his life." Ultimately, his motives are banal. The key to Iago's success is that people trust him because he tells them what they want to believe because he is perceptive to their weaknesses.
Iago carefully maintains a veneer of "honesty and trust" but like many people, his outward appearance belies a inner deception. Iago is commonly referred to as Machiavellian, a term coined for Prince Machiavelli. Machiavelli is famous for his political treatise, "The Prince" which espouses, among other things, that the ends to power always justify the means.
Othello is particularly susceptible to Iago's ploys. Iago himself is so noble and unsuspecting of villainy that he easily plays into Iago's hands.
Iago will use anyone and anything to get what he wants. He uses Rodergio, for example, encouraging the young man to continue his pursuit of Othello's wife. He then plots to make Othello believe that Desdemona has been unfaithful with the lieutenant. Iago plies Cassio with wine, then encourages him to pick a pick a fight with Rodergio. "In his shame," says critic Homer Watt, "Cassio falls readily into Iago's suggestion that he beg Desdemona to intercede on his behalf. It is the villain's trap."
By constructing situations in which Iago appears blameless and other fall, this cold, egotistical man stays above suspicion.