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.
Talking to your coach. This is a habit where you can learn to be effective 100% of the time. Pay attention and you will know when you interrupt people unnecessarily. Once a day or throughout the day tell your coach why you have—or haven’t—listened without interrupting. Making the journal entry will stimulate your thinking about the circumstances under which you do in fact avoid interrupting others. Your coach will ask questions, not expecting an answer, but rather to make you aware of cues and reinforcers that drive the habit.