Fellow speaker,
Professional speaker Michael Carusoe suggests you can get more energy and power in your voice if you pretend you are yelling at a dog. The trick is, when you do the "dog yelling" keep your face smiling and relaxed. Imagine you have a dog and it just did something bad. Then say what you have to say as if you are yelling at the dog, but keep your face smiling and relaxed.
Dog-angry,
Tim Wilson
Professional Speech Coach
Free speaking tips at: http://speakingquicktips.blogspot.com