Research your topic of discussion and create an outline of what ideas you wish to cover.
Make slides, if applicable, in Microsoft PowerPoint or your own favorite presentation software.
Talk through your presentation many times before presenting. Open your slides and actually click through them speaking your part out loud.
Sleep well the night before your presentation. Do your best to get eight hours of sleep.
Eat a good breakfast the morning of your presentation.
Relax before and during your presentation.