If you use overheads or other media, do not clutter the slides. Four or five thoughts per slide. Thoughts should be in bullet fashion, not complete sentences. You should take the bullet and enhance it, extend it, clarify it. If all you say is what is on the overhead, there is no reason for you to be there or talk.
Preparation is the key to successful presentations.
Know who says what when. Rehearse it thoroughly. Think it through in your sleep or during your drive to school. Visualize yourself presenting your presentation from introduction to conclusion. When you finally present, you will think to yourself that you have already done this and it is almost deja vu.