I am a big fan of the comic strip, XKCD. The best humor is observation of the small ironies and truths of everyday life. Randall Munroe is brilliant at it.
Having worked in the past in the field of ABE, I am particularly sensitized to the fragile confidence with which adult learners often struggle. This is also true in workforce training, where people's jobs and professional futures may be on the line. Most everyone struggles with what I call "the imposter syndrome." Leaders and trainers must know there are no insignificant comments or tone of voice.
Early wins built confidence and engagement. Use every opportunity to encourage both. The more learners can relax in to trusting you and the experience, the more they will learn.