Vocal coach Kate Peters suggests when practicing speaking you first make an "mmmmmm" sound so that you feel your voice resonating in the front of your face. After you feel that resonance, keep the feeling while you begin giving your speech (e.g. "Mmmmmmmmmmmm If you have ever driven a car...). This will build up vocal resonance and depth.
Vocally,
Tim Wilson
Professional Speech Coach
Free speaking tips at: http://speakingquicktips.blogspot.com
