Did you know that 55% of your message is actually conveyed by your body language? That means that the way you present yourself during your talk is actually more important than what you actually say.
Think about it. Do you feel motivated by a speaker that has little energy, doesn't make eye contact or looks nervous or confused? Of course not! It doesn't matter how good the message is. If the body language is sending a conflicting signal, that signal will always win.
So, what should you watch out for? A lot of people define body language as the gestures you use. In reality it is much more. In addition to gestures, your body language consists of your posture and movement and facial expressions.
When you are on a stage in front of a lot of people, you need to exaggerate your body language so it can be seen. Keep your gestures above your waist and don't be afraid to stretch your arms out more than you normally do. All the stage is your world, so to speak. Take advantage of it.
Your facial expressions should also match the message you are sending. Make sure to make eye contact with individuals in your audience as well. Don't just skim over the sea of heads.
Take note of your posture. You should ooze confidence, even if you don't completely feel that way. For a longer discussion on posture, see this earlier post. Don't be afraid to move around the stage either. It's OK to walk around - movement between points can be especially helpful to signal a change in your talk. Just be careful you don't start pacing back and forth on stage. That can be very distracting and can make you look nervous.
Your body language constantly sends signals that you might not even be aware of. Video tape yourself speaking so that you can see what messages you are sending. You might be surprised!