Design areas for the students and the instructor in a way that creates the desired dynamic. An instructor at a podium or a desk at the front of the classroom creates a traditional lecture type class dynamic. An instructor who sits with the students in a circle or around a table creates a more communal and collaborative dynamic.
Establish the rules for interaction. In the first class lay out the system for how you will interact with the students. If discussion is the primary focus then each person should talk the first day, and a way of taking the floor should be established (like raising a hand). If the class is more instructional, then those rules should be established, or if it's a lecture type class address how questions and comments will be handled.
Consider the ambiance and environment of the class. Every classroom can harm or help the kind of environment the teacher wants to establish. For example it's very difficult to have a discussion based seminar in a lecture hall or a hands on instructional class in a meeting room. Additional environmental factors, like ambient noise, temperature, lighting all can contribute to how the class will run as well. All of these variables should be considered.
Gather the materials necessary for each class. It's important that the class materials are accessible to the students. Especially in a hands-on instruction based class it is important to consider what tools each student must have to participate.
Hold class.