This is an excerpt from http://www.sovereigngraceministries.org/Blog/post/Meet-John-Piper.aspx >
What single piece of counsel (or constructive criticism) has most improved your preaching?
Don’t preach in a way that a Muslim would approve. Preach a divine crucified Christ.
What books on preaching, or examples of it, have you found most influential in your own preaching?
Spurgeon, Lectures to My Students; Lloyd-Jones, Preaching and Preachers; John Stott, Between Two Worlds; Graeme Goldsworthy, Preaching the Whole Bible as Christian Scripture.
What single bit of counsel has made the most significant difference in your effective use of time?
A great tree will fall with many small chops. Pray for daily grace to keep chopping.
What single bit of counsel has made the most significant difference in your leadership?
Lead by helping people see the same truth in the Bible you do so that commonly perceived truth is the fabric that binds together. When truth is not the bond, power moves are inevitable.