I read Speak to Influence by Susan Berkley and it was just O.K. There were some good practical exercises for warming up vocal chords and tongue twisters to help enunciation. There was also a section on leaving voice messages, which I found particularly helpful. (My favorite: Leave a message just with your name and number and without details, creating a sense of mystery.) Overall, though, I didn’t see anything over and beyond what I learned in my Oral Presentations class. There are no secrets to good public speaking. Learn the basics, such as eliminating fillers. Record yourself and watch yourself. Practice, practice, practice. That’s most of it.