Being a good listener is not as complicated as most people think it is. When having a discussion with someone, make sure to let him know in a subtle manner that you are paying attention to what is being said.
Don't be afraid to nod your head and chime in with the occasional "I see," or "I understand," or any other verbal cue that shows the other person that you are indeed listening attentively. Also, feel free to ask questions (preferably non-threatening ones) if you are unsure of what the other person is trying to communicate. Finally, do not interrupt when someone else is speaking. Interrupting someone in mid-sentence is extremely rude and will count as one strike against you in just about any social setting. Proper etiquette is suggested at all times