No Fear Shakespeare: Othello: Act 1, scene iii

330	To get his place and to plume up my will
	In double knavery. How? How? Let's see.
	After some time, to abuse Othello's ear
	That he is too familiar with his wife.
	He hath a person and a smooth dispose
335	To be suspected, framed to make women false.
	The Moor is of a free and open nature
	That thinks men honest that but seem to be so,
	And will as tenderly be led by th' nose
	As asses are.
340	I have 't. It is engendered! Hell and night
	Must bring this monstrous birth to the world's light.

get his position and use him to hurt Othello at the same time? How? How? Let's see. After a while I'll start telling Othello that Cassio is too intimate with Desdemona. Cassio is a smooth talker and a good-looking guy, the sort of man that people would expect to be a seducer. The Moor is open and straightforward. He thinks any man who seems honest is honest. People like that are easy to manipulate. So it's all decided. I've worked it out. With a little help from the devil, I'll bring this monstrous plan to success.

Exit

He exits.