Before you begin, you must have a clear course plan that specifies what the course covers and what materials are going to be used. Your plan should list in order the topics to be addressed and budget an appropriate amount if time to each topic.
A good teacher is prepared to teach. This means having an idea about what will happen in class, but often it also means being able to respond to whatever starts happening and being willing and able to do something different than one planned, all in service of the students and their language acquisition, and this comes from being a certain kind of person with certain go-to practices.