We all get stage fright when making a presentation. Fortunately, for most of us that nervousness can be controlled.
One trick to relax yourself is to use a conversational anecdote as a opening. For example, perhaps you are at a conference and you’re the next speaker. In your open you can talk about the general chatter that you’re hearing, or some famous celebrity you bumped into. It’s not long open, perhaps 3 or 4 sentences, but it is enough to relax you so that when you launch into your real opening you are less nervous.
The nice thing about the conversational open is that it is usually of interest to the audience. As long as it doesn’t go on and on.
Any kind of talking prior to going up to the podium will also be a big help in relaxing you. Just chatting with people in the audience, particularly about what you will be presenting, will make you more calm. And, don’t forget to smile and use good posture. These are physical signs from your body to your brain that you are feeling confident.