This is an attainable wish. It will require a lot of self control and practice though. Don’t just speak immediately whatever comes to your mind, try to think of the major points you plan to hit before you speak the first word.
Another big tip is one that newscasters use: limit your use of “um,” in conversation. When you pause while speaking, make sure to make it a silent one. The “um’s” will make you sound less intelligent.

Thanks. Good advice.