Nothing helps a student orient to your class like you being prepared and comfortable. This is not always the easiest state to achieve however, and you will need to work at it.
Students need a clear goal to pursue. The first class period is your time to help them see that goal and to set the stage for the semester. This is the time to describe what they will be able to take away from your class if they diligently work to master the content. It is also a time to demonstrate a bit about your teaching style by incorporating how you will teach the class in the first days. You may not feel prepared to be the master of this data. But you probably know more about this topic than the students do.
The bottom line is that the students are there to learn from you and you are there to teach. This simple relationship gives you the authority to assume the role of instructor. Do not second guess yourself on this. You were picked for this role because you demonstrated an understanding of the content. Give that understanding to your students.
Seminars offered by the Walker Center for Teaching and Learning may help you master new teaching techniques.