Take a look at some of the most famous speeches throughout history, at currently popular politicians, and even at local newscasters. You'll find that most of them have lower tones of voice, and this is no coincidence.
People tend to view speakers with lower speaking voices as having more authority and confidence.
As much as you can, practice speaking in a lower tone of voice.
Don't force yourself or you'll sound unnatural, but if you can get yourself a tone or two lower, it can make a real difference.
- Jayson Demers (modified by Amr Badran)