You might try Toastmasters. Once you get past the first few "nervousness" lessons they focus on how to convey meaning with speech. Every chapter is different, so YMMV. Several of the speeches you have to prepare cover persuasion, motivation, and how to structure a speech so that everyone remembers exactly what you want them to remember. They teach through having you give a series of 5-7 minute speeches, but I've found the practice helpful beyond giving a formal talk.