Adult learners bring many skills, insights, attitudes and other life experiences to the classroom. Failing to recognize the dynamics at play and build this into instructional strategy often results in anger, disappointment, apathy or disregard of your training effort or ability. Get to know your audience and their moods and expectations as of today. Don't apologize for or assume the students already know the information to be taught. Begin with a full explanation of what is to be taught, then assess the audience for their level of that knowledge.
Most groups vary in their sophistication with every topic.
Take advantage of students who have experience with the information and beware of those who only think they do. If you feel the need to apologize for not being prepared or not knowing your topic, do it and then leave the room. Be organized, set clear expectations and follow a well designed lesson plan. Never begin teaching a topic unless you have convinced the audience there is a need for them to learn the lesson to be taught. Tie the lesson to their experiences and job-related needs.