Take the time to articulate every work of each sentence clearly, while maintaining eye contact with your audience. It is here the audience expects to be provided with the most important information. Nervous, hurried speech often leads to inaccurate articulation. Take your time and do not speak faster than your normal conversational speed. Monotony is the greatest enemy of a scientific presentation.
Plain silence is preferable to mere noise.
Slowing down is a remedy for 90 percent of most speakers' problems. Looking straight at members of the audience establishes the notion that you are talking to them, not just in front of them. Structure your viewgraphs in such a way that the images are able to convey most of the story by themselves, even if you are hard to understand. Posture and gestures. Stand straight up.