Startup Journal has a good post on how to improve your public speaking skills.
I’ll just add one more suggestion:
Read to your kids.
This can be even more effective if you use funny voices, and try to convey the emotions of the story to your “audience”. Kids are pretty forgiving, they’re patient when you stumble over words or lose your place. For added technical challenges, read in a dimly lit room, or sit on the floor facing your “audience” with the book on the floor in-between and try to read upside-down. You will stumble, and stutter, and you’ll learn to get through the distractions.
One Man Shouting 