This kind of preaching is most helpfully done when a minister follows the logic of the Scriptures, systematically preaching chapter by chapter and verse by verse through entire books of the Bible. This helps ensure that a congregation hears what God wants them to hear, and not simply what their minister thinks they ought to hear.
But expository preaching is not so much a method as it is a mindset. A minister who sees himself as an expositor knows that he is not the master of the Word, but its servant. He has no other ambition than to preach what the Scriptures actually teach. His aim is to be faithful to God’s Word so that his people can hear God’s voice. He himself is only God’s mouthpiece, speaking God’s message into the ears of God’s people, and thus into their minds and hearts. To that end, he carefully works his way through the Scriptures, reading, explaining, and applying them to his congregation. On occasion he may find it necessary to address some pastoral concerns in a topical fashion, but even then his sermons come from his exposition of particular passages of Scripture. Rather than focusing on his own spiritual experience, or on current events, or on what he perceives as his congregation’s needs and interests, the minister gives his fullest attention to teaching what the Bible actually says.
If you care to read the rest of the interview, go here: http://unashamedworkman.wordpress.com/2007/04/11/ten-questions-for-expositors-ryken/