I've been meaning to get round to writing proper reviews of these two books for quite a while now. So just in case I never actually get round to reviewing them, I thought I'd just give a quick recommendation.
Spirit Empowered Preaching: Involving the Holy Spirit in Your Ministry, by Arturo Azurdia, looks at the role of the Holy Spirit in preaching. Azurdia not only looks at the function and need of the Holy Spirit's activity in preaching, but also points to some helps and hindrances to a Spirit-empowered sermon. He helpfully reminds us that unless preaching glorifies Christ, it will not be accompanied by the power of the Holy Spirit.
Why Johnny Can't Preach is a completely different type of book. Whilst Azurdia focused on the Holy Spirit's role in preaching, Gordon focuses on part of the preachers role. Gordon's thesis is that many contemporary preachers simply can't preach due to the influence of the media culture in which we live. Electronic media have changed our communication patterns, meaning that we are no longer accustomed to discursive speech. Basically the problem boils down to the fact that most people in the pew cannot tell you the point of the sermon after it has been delivered. Therefore many sermons fail on the level of communication. Gordon also turns aside for one chapter to look at failings in the content of preaching. Gordon not only offers critique, but also offers the hope that it is possible to overcome these shortcomings and preach well. This is not simply a book on effective communication, and at only 108 pages deserves a thoughtful reading by preachers.