Volume - We need to be aware about the volume at which we speak. Too soft and people may not hear what we've communicated or would be straining themselves to hear us, which could irritate them further. If too loud; that too could pose a problem. For people would be striving to get away from you. Furthermore, if we speak too loudly, it might be interpreted as aggressive and may antagonize the people from whom the message is intended. A raised voice suggests intimidation or bullying.
Pitch - We also need to ensure that we talk at the correct pitch. Too high and it can sound piercing and uninteresting; too low and it can become inaudible. We also need to guard against a tendency to lower our pitch at the end of a sentence.
Speed - We think faster than we speak and we speak faster than we can hear and comprehend. Hence, we have to ensure that we talk at an adequate speed so the intended recipient can hear and understand us completely. We further would need to speak at a lesser speed if there's note-taking involved.
Vocabulary - Use words to express, not to impress. Take due care to use simple words in order to get your message across. Exercise sound judgment when using acronyms and technical words and offer explanation. Also, be aware of words that mean different things in different cultures, countries and languages.