Practice the demonstration first, and should you notice multiple students making similar mistakes, address the class as a whole. 

Should a class time be longer than 2 hours- have an interactive activity planned for students. It is positive for students to feel like they can rely on each other. 

A syllabus is like a contract between the instructor and students- be as specific as possible with details so the contract/syllabus can be referenced at any time if need be for clarification throughout the term. 

Continuously further your craft of education so you can be a better instructor and share knowledge that you have.