Explain to your candidate how to ask further questions in a conversation in order to really understand the other person.
Ensure that your candidate does not interrupt other people when they are talking.
Encourage your candidate to take notice not only of what another person says but also of what he signals with his body language, facial expressions and attitude. Are the words and signals concurrent?
Encourage your candidate to ask ‘open questions’: questions that cannot be answered with ‘yes’ or ‘no’ (and often begin with ‘who’, ‘what’, ‘where’, ‘which’, or ‘how’).
Encourage the candidate to practise his listening skills outside of work as well. Involve family and friends to provide feedback.