The purpose of communicating science is to aware scientists communicate their work with others effectively. As an example, one should note that when giving a talk, this is not just that person speaking, but the speaker should spontaneously interact with audience. It is accomplished not only by talking clearly, but also adding some extra elements to make it go as you are talking. It includes facial expressions, tone of voice of the speaker and acting. This body language helps to add an emotional content to the talk. Hence, communicating science is not intended to be skillful while giving a speech but also to include other sorts of communication with people. It is even more difficult because of the limited words that can be used to convey the purpose.
I think a successful communication consists of two parts; first is to organize the content and think about how it should be delivered and second is how to deliver it to the audience. In fact, these two parts are inseparable and should be managed during the time of communication.