In active listening, what do you do to obtain information that may be missing from the message

You should try to make eye contact often, but not the whole conversation; you should be presenting a sense of actually focusing on what the person is telling you, rather than just hearing what they are saying just because you are there. You should also ask questions in order to receive clarification of what was just said from the speaker. you most importantly shouldnt be into foreign topics, but rather build up on what you hear.
hope this helps