We have to remind ourselves that the effectiveness of a priest's preaching depends mainly on the state of his spiritual life. More than his intellectual caliber and his speaking and entertaining skills and other charms he possesses, it's in the health of his spiritual life where the people can truly hear the word of Christ.
Remember that Christ told his disciples: "Whoever listens to you listens to me." (Lk 10,16) These words clearly presume that the priest should be identified with Christ so his preaching would be the preaching of Christ, and not just his alone.
While all his human powers and talents have to be used for preaching, one has to see to it that that these powers and talents get truly inspired by the spirit of Christ. In short, the priest has to assume the very mind and heart of Christ when he preaches. Otherwise, he will just be preaching himself to the people. And that would be very funny and anomalous.
All the legitimate concerns for him to be effective in his preaching, like he has to be identified with the people, to be innovative in order to flow with the times, etc., should come as a consequence of his indispensable identification with the living Christ to whom he is sacramentally conformed.
Remember that Christ is the perfect mediator between God and men. The priest can only be a good mediating preacher to the extent that he becomes another Christ.
The priest should always remember the radical identity he has. He is no one other than Christ, head of the Church. Even when he is playing sports or on excursion, this awareness of this identity should never be lost.
Imagine if he is truly another Christ, if he has the very mind and heart of Christ. He would never run out of things to say, he would know how to read minds and the signs of the times, he would be full of goodness and mercy!
For this, he should always be praying, or at least conscious he is in the presence of God. Everything in his life, no matter how small and insignificant in human terms, should be a material for his abiding dialogue with God.
It is important, therefore, to do everything just to be another Christ not only in name and title, but most especially in vivo! He should avoid simply being some kind of bureaucrat, a Church official, a scholar, an expert in something. He has to be another Christ, nothing short of that!
When one strives to be another Christ, even his limitations and mistakes can be very useful. The opposite is also true. When one is not truly another Christ, even the best qualities and talents he has can be a danger to him and everybody else. Let's remember what St. Paul said about this.
"Brothers, consider the time of your calling. Not many of you were wise by human standards. Not many were powerful. Not many were of noble birth. But God chose the foolish things of the world to shame the wise. God chose the weak things of the world to shame the strong. He chose the lowly and despised things of the world, and the things that are not, to nullify the things that are." (1 Cor 1,26-28)
The path to be another Christ is that of humility that will always nourish our faith, hope, and charity, in short our spiritual life. We need to travel this path for one to be a good and effective preacher.