You need to listen with your whole being. Not just hear what your spouse is saying while preparing your own response in your head. Your non-verbals should show that you are interested in his/her story, turn and face your partner and don’t cross your arms or legs. Be open.
Say things like "Yes, I understand. Tell me more." To make sure you have truly understood each other, try to paraphrase what your partner has expressed. It can go like this: "OK, from what I understand, you mean…"