Mean what you say and say what you mean
Is the meaning of your message clear? A great opening to any communication is "I want to discuss xyz because…. followed by "whatever" after the opening. If you use this phrase you alert the listener to the topic and importantly your motivation for the discussion. People can't guess what you're thinking. you have to let them know.
Keep it simple
Are the words you are using appropriate to the listener? Avoid big words they can confuse the listener. Avoid jargon at all costs.. its just dumber than mud.
Is your attitude betraying your purpose
The tone and pitch of your voice will have a great effect on your listener. Keep it calm an even so you are not destroying the ability to listen for the other party. A big problem I find is page… slow it down give the listener a chance to absorb what you are saying. Speaking too quickly will convey impatience and even the other person's belief in what you are saying. If you rush you can jeopardise the empathy the listener will have for both you and your message
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