Here's a simple trick to get yourself in the right mindset for your presentation. It makes you feel good, it makes the audience feel good, and you already know how to do it: Smile.
Some studies have suggested that when you make a face like smiling or frowning, your body goes through physiological changes as though you were feeling the emotion attached to that face. That is, when you fake a smile, your body thinks it's happy.
In fact, in one study, "Participants who were more self-conscious showed greater changes in mood following making the positive or negative expressions."
The next time you give a presentation, as part of grounding yourself before you speak, make sure to look around the room and smile at the audience. You might find yourself feeling more relaxed. And when you smile at the audience, they will smile back, giving you even more positive energy. It's a win-win.