Allow your senses to be aware of everything that is going on as you speak, and adjust your presentation accordingly. Often my best material comes from what is happening in that meeting. Tony Alessandra agrees. When you ask questions of the audience, you may get answers that you weren't expecting, and you have to play off of it. Some of my best lines come from the audience.
Actors break a scene down into beats and establish variation for each beat.
Speakers can strive for variation in emphasis, movement, volume, energy level, material, etc. Variation can occur in the volume and tone of your voice. Pausing is a form of variation. And don't forget to build variation into your body movement. Variation is an effective technique for keeping them with you.