The language we use can encourage interaction and participation in the class. Communication that proceeds only in one direction invariably leads to failure to communicate. Effective communication is two-way. Classroom interaction exists within a context of interaction outside the classroom. Relationships outside of class enhance the class.
Nonverbal signals are important.
Eye contact is important when teaching. Also, people often frown when listening and a student may misinterpret the frown as disapproval or disinterest. Try smiling or telling them you are listening. A lecture benefits from intense moments and relaxed moments. Attention span is at best 20 minutes.