Following on from the post below, here is Dr. Lloyd-Jones on seeking the power of the Spirit in preaching. This is the final, rousing exhortation in Preaching and Preachers:
What then are we to do about this? There is only one obvious conclusion. Seek Him! Seek Him! What can we do without Him? Seek Him! Seek Him always. But go beyond seeking Him; expect Him. Do you expect anything to happen, when you get up to preach in a pulpit? Or do you just say to yourself, 'Well, I have prepared my address, I am going to give them this address; some of them will appreciate it and some will not.?' Are you expecting it to be the turning point in someone's life? Are you expecting someone to have a climactic experience? That is what preaching is meant to do. That is what you find in the Bible and subsequent history of the Church. Seek this power, expect this power, yearn for this power; and when the power comes, yield to Him. Do not resist. Forget all about your sermon in necessary. Let Him loose you, let Him manifest His power in you and through you. I am certain, as I have said several times before, that nothing but a return of this power of the Spirit on our preaching is going to avail us anything. This makes true preaching, and it is the greatest need of all today - never more so. Nothing can substitute for this. But, given this, you will have a people who will be anxious and ready to be taught and instructed, and led further and more deeply into 'the Truth as it is in Jesus'. This 'unction', this 'anointing', is the supreme thing. Seek it until you have it; be content with nothing less. Go on until you can say, 'And my speech and my preaching was not with enticing words of man's wisdom, but in demonstration of the Spirit and power.' He is still able to do 'exceedingly abundantly above all that we can ask or think.'
From Preaching and Preachers p. 325, Hodder and Stoughton, 1985.