I stumbled across some interesting free PDFs by Toastmasters International that are designed for public speakers and presenters, but there is much good info here on improving your speaking voice and your body language in personal interactions. I thought they might be of interest to sedditors.

Your Speaking Voice: Tips for Adding Strength and Authority to Your Voice

Gestures: Your Body Speaks - How to Become Skilled in Nonverbal Communication

The have other free resources here but these two seem the most directly relevant to seddit.