They either listen to someone else preach or do the preaching. I, like Miller, have to acknowledge that the experience of both often falls below that which these verses below describe. His letter tells of using these for his morning devotions.
1 Cor 2:4
1 Thes 1:5
He then writes:
"Power in preaching comes comes from a strong faith that is qualified by wisdom. Preaching is faith speaking; that is what it means to preach in the power of the Spirit. And faith and confident praying are two sides of the same coin. Basically, I am convinced that men who do not make praying their first priority in life and ministry should not preach or pastor. As preachers they will be confusing models of a Christian man, and as shepherds they will be not show willingness to die for the sheep. Their spirit will inevitably drift in the wrong direction."
So the answers is to pray. If you are a listener pray for your preacher, if you are a preacher pray for yourself and those who have to listen to you.
We all need more power.