[abibibo]

As others have said, practice is essential--especially in front of other people or at least a video camera.

Also, become comfortable with silence. Standing front-and-center in a crowded room and staying quiet for even a couple moments can be terrifying at first--much more difficult than actually speaking in public. As a result, many inexperienced speakers end up rushing through their entire speeches, reciting word for word what they practiced without emotion or even an awareness of what they are saying, too afraid of silence to stop for even a moment.

In reality, such pauses do wonders in not only breaking up the cadence of your speech to grab the audiences attention, but also allowing you the opportunity to collect your thoughts and contemplate what points you want to make on your next topic or what points you need to add before moving on. Try forcing yourself to pause for a couple seconds as you put up each new slide.

Although I usually like to have the first few sentences of a speech planned out verbatim to get the ball rolling smoothly, I still make a point of just standing quietly for about 10 seconds after the introduction. It's enough to get me comfortable with the feeling of silence so that I'll be able to pause and collect my thoughts later on, and just long enough to make the audience curious and attentive--ideally causing everyone to look up and be alert as your start into your speech.