You each get a turn to talk to the other for half an hour -- no more, no less.
When you're talking, you can only talk about yourself, not about your partner or the relationship. Focus generally on your emotions, your needs, what you've learned from books or films, your friends, your job, what you like about yourself, what you don't, how you're enjoying life and how you're coping with life's struggles.
You're not allowed to interrupt or even comment on what's been said. Your job is simply to listen and try to understand the person talking.
Watch your facial expressions and body language. Nod supportively. Say, "Uh-huh." Smile encouragingly. Sitting there sulking or with a thunderous expression is going to thwart the whole exercise.
If you really, really, really must comment on something your partner's said, wait a full 24 hours. Then, if you still can't help yourself, you're allowed 10 minutes max. One other catch on replying: The comments can only be positive. If you think there's a problem, for instance, outline it quickly, then spend the rest of the time talking about possible solutions. For example: "Your comments about your close friendship with your female coworker have made me realize we need to discuss boundaries," rather than, "I can't believe you've been spending so much time with Anna without telling me, you miserable bugger."
After doing this exercise, don't be surprised if you both feel a little unnerved. You've probably just discovered things about your partner you didn't know -- and that's why you feel slightly nervous. Who is this person? You thought you knew him inside out! What a shock, eh? But after all, you don't own each other and can't control how you both feel. Relax and go with the uncertainty. Taking your partner completely for granted is what kills most relationships. It does both of you good to not feel 100 percent sure of each other.
Repeat this session once a week for a month, and you'll find you start to listen properly without it having to be a structured exercise.