These techniques are described in the following:
Look for signs of resistance, confusion, or frustration among learners, such as facial expressions, other body language, or non-participation in activities.
If learners are keying, listen for errant keystrokes, beeping, negative comments, or other signs of discontent.
Ask learners how they're feeling about the pace and clarity of the presentation. Examine the individual progress of learners during exercises. Do they understand the material? Does a concept need to be re-explained
Ask for questions and comments and then address the issues in a timely manner. You can promote participation if you handle questions positively and enthusiastically.
Finally, be sure that that your verbal and non-verbal communications are free of bias. You don't want to communicate any sexual, racial, religious, cultural, or age discrimination.