Professor Patrick Winston of MIT used to give a one-hour talk about how to speak. Though Professor Winston is no longer with us, his talk still is. If you want to get better at speaking, even if you’re an experienced speaker, I recommend taking the hour to watch the recorded video:
The YouTube recording does have a link to the MIT OpenCourseWare page, but it simply contains a link to the video and an outline of the talk.
If you’re on the fence, Professor Winston remarks at the beginning of the talk that you’re ability to speak well is a necessary skill to advance. Part of his talk covers interviewing for jobs so when he said speaking, he meant in all forms professionally, not just someone giving a talk.