Find and check out your local Toastmasters group. There is a biannual membership fee, but this organization's sole purpose is to improve the communication and leadership skills of its members. The group not only helps you improve your tone, but also teaches you how and when to use hand gestures to emphasize your points. If you complete 10 speeches, you will be a Toastmaster certified speaker. Usually, the groups are very friendly, so it's an effective place to improve your speaking and presenting skills.
Read. Books help to teach you more about the world as well as help improve your vocabulary. Having a large vocabulary gives you a bigger tool set to work with when choosing your words. The more you read, the more ways you learn to express yourself.
Practice your speaking in front of a mirror, record yourself with a camcorder, or practice with a friend and ask for her feedback. Be persistent.
Smile and practice making eye contact with your audience. This allows you to convey a friendly attitude and develop credibility.
Stand erect but not overly straight to convey confidence. Use self-deprecating humor to ease tension and gain sympathy.