We all can communicate well with some people and not equally as well with some other people. Learn from your strengths. Learn from your successes. Learn from your best moments.
Your own best moments are your best teacher. So the question to ask yourself is, "With whom do you communicate well?" What can you learn from the way you speak to those people? Very likely, the way that those people speak to you and treat you has an influence on the way that you communicate with them. Even so, awareness of what you personally do right when you speak to them can help you speak better with the people you find difficult to interact with.
Moreover, if you ever have a difficult time communicating with someone that you sometimes communicate well with, ask yourself, "What exactly did I say and do when I communicated well with this person in the past?"
(from Rabbi Zelig Pliskin's book: Harmony with Others, p.72, www.artscroll.com)