A really good teacher knows the material that they are teaching. This knowledge should be practical as well as theoretical. Knowing about how chemicals react from personal experience I can more vividly tell them about these reactions. The teacher must also have the skills to present the material in a way that the students can understand it. I have found that students learn in different ways.
Some students like to work in groups.
Some are very theoretical. Some want practical examples and some like demonstrations. It is impossible to perfectly teach a large number of students because each student is different. However, I try to do a little of each of the above methods to hopefully reach out to each and every student. I give some theory, some demonstrations, some applications and allow some group learning experiences.