Listening without interrupting, or, better yet, active listening, is perhaps the single most important social skill. Paying close attention to other people when they speak is a gateway to "social intelligence," the general ability to understand and work with others.
The verb listen is used a lot, but its true definition, to pay attention, heed, is often overlooked. Be mindful of the need to pay attention to and heed, AKA listen to, what the other person is saying. Become a better leader, colleague, and, yes, friend or intimate, by simply looking at the speaker and listening attentively without judging or interrupting. Train yourself to never, or at least rarely, interrupt.
We have two ears and one mouth, all with their own pathway to the brain, and it can be argued that the ears-to-brain circuit is the most important one for effective communication. An amazing variety of books on all sorts of subjects from sales to leadership to success in marriage emphasize the importance of listening. For example, Craig Lawn’s Shut up and Sell: How to Say Less and Sell More is a classic in the world of sales where such things as the best talk/listen ratio (e.g., the customer should talk twice as much as you, a 2/1 ratio) are hotly debated.