Once you believe God is calling you to preach His Gospel, the first step is presentation of yourself to your pastor. Tell him of your consciousness of call. He can give you not only experienced counsel, he can also inform you of any formal process you should follow in your church. Your next step is preparation . A call to preach is a call to prepare.
Preparation is even more important for a physician of souls .
Develop your spiritual disciplines, especially those of the Word and prayer. Devote yourself to your local church. Find a place to teach there. Study the Bible and theology as much as you can. Seriously consider enrolling in a solid seminary.