Nonverbal communication speaks volumes when we have a hard time saying what we really mean.  Sometimes we're not even aware that there's a disconnect between what we're saying and what we're doing.
When it comes to listening to someone, be aware of both your body language and the person who's talking.  Are their arms crossed, are they tapping their foot, are they sighing a lot?  If so ... are you really listening to them?
Remember, communication is a two way street!