Your audience starts reading you before you say a word. How you walk to the front, how you stand, where your hands go. If your words say "confident" but your body says "please let this be over", the audience believes your body.
The good news is that body language can be learned.
Stand like you belong there
Feet hip-width apart, weight evenly balanced, knees soft. Avoid shifting from foot to foot or crossing your legs while standing. A stable base makes you look, and feel, grounded.
Let your hands help
Many speakers do not know what to do with their hands. Pockets, crossed arms and clasped hands all look defensive. Instead, let your hands rest loosely at your sides or at waist height, and use them to gesture naturally when you speak, the way you would with a friend. Open palms signal honesty.
Move with purpose
Pacing back and forth drains attention. Standing frozen looks nervous. The middle path is purposeful movement: move when you change topics, then stand still while you make a point.
Use your face
Your expression should match your message. If you are telling a funny story, let yourself smile. If you are making a serious point, let your face show it. Many nervous speakers wear one fixed expression throughout.
Eye contact
Look at individuals, not the whole room. Hold each person's gaze for a complete thought, then move to someone else in a different part of the room. People feel spoken to, not spoken at.