Ajith Fernando has some penetrating words for preachers on the importance of taking sermon preparation seriously in his article called Passionate for God? Or addicted to mediocrity? This quote will give you a flavor of his message:
If we are going to preach then we must fashion our schedule in order to give us time to prepare. If, for some reason, that becomes impossible, then perhaps we will have to cut down on our sleep in order to prepare adequately to represent God well. And if we die early doing that, we would have died for a great cause!