Being aware of other people's emotional cues such as body language makes you a better speaker
an effective listener.
understand your audience,
keep eye contact.

Explanation:

If i'm being honest, 'understand your audience' and 'keep eye contact' are very good choices that makes me doubt the answer I had in mind. But it for sure is one of those two.

Imagine your on a stage having to present something or something else and then you do something they find funny, you'd want to look at their reaction to the next funny thing you do, right. (keep eye contact) or (understand your audience)

get what i mean :|