Do some deep breathing. Count to three breathing in through the nose and release counting three through the mouth.
Focus on your audience, not on yourself. A message that matters to your audience is about your audience.
Visualize your success. Picture how it will look and feel to hit a grand slam presentation and relieve some worry.
Use Humor. Once you get people laughing, they are listening.
Don't fear a moment of silence. Sudden silence has the same effect as a sudden loud noise. It alerts your audience and makes them attentive to what you say next.