I just completed two days of presentation skills training with a large government agency and wanted to briefly share some thoughts about body language and nonverbal communications that came up repeatedly.

First, it is essential that presenters think about and prepare for what they want to do with their body during a presentation. We tend to spend most of our time planning for WHAT we are going to say, but completely neglect HOW we are going to say it. The way you stand, your facial expression, your ability to make eye contact and what you do with your hands can each amplify or distract from the potential impact of your presentation.

The way you stand. The most powerful way to stand is feet about should width apart, shoulders square and hands at your sides. Try standing that way. Do you feel uncomfortable? If you do, it is because you are defenseless -- literally and figuratively. If something was coming at you, there is little you could do about it. But that is what makes it such a powerful stance -- you HAVE to be confident, comfortable and in command to stand that way in front of an audience. If you catch yourself shifting your weight to one leg or the other -- of fidgeting side to side, recognize that's something you can work on. 
If you feel compelled to move around, try to make those movements purposeful and not just random. You don't want to distract the audience, but walking slowly from one spot to another and then staying there for 30 seconds or so can make you look thoughtful and can help to calm your nerves. Just be sure you don't start pacing. That's why it is important to stop and stay in one place for at least 30 seconds. Pacing makes you look nervous.
Your facial expression. For the most part, speakers are presenting POSITIVE information. It is rare that a speaker gets in front of an audience and describes how lousy things are. Yet, you would never be able to tell that from the expressions on the faces of most presenters. If they don't look downright miserable, they have neutral expressions that don't contribute positively to the presentation. If you expect the information you are presenting to be interpreted as being positive, you need to deliver it with a positive, open facial expression.
The default facial expression from the time you are being introduced to the time you sit back down should be a smile. This can be a challenge for those who purse their lips and/or furrow their eyebrows when they concentrate. These expressions are perceived as negative by the audience and can drown out the positive message you intend to send. If you catch yourself furrowing your eyebrows or feel you smile fade away in the midst of the presentation, those are areas to improve. The last thing you want to have happen is finish your presentation and have the audience be confused about whether what you said was positive or negative.

Your ability to make eye contact. The next time you see a baby who can't yet speak, pay attention to the baby's eyes. During those early months of life, a human brain soaks up a tremendous amount of information and most of it comes through the eyes. But isn't it interesting that in the midst of all of that information gathering, a baby's eyes will stick to your eyes once they meet? And they will stay stuck on your eyes so long that it can begin to freak you out!
What babies know if that a great deal of information about a person can come from "reading" their eyes. They can project happiness, sadness, excitement, boredom, sickness, health, confidence, shyness, truthfulness and so much more. As we get older, we continue to rely on eye contact to round out our interpretation of events as they unfold. For this reason, it is essential that a presenter make and hold eye contact with members of the audience. If you are presenting to a group of 10 or fewer, make a point to make and hold eye contact with each person.
Don't allow your eyes to dart around quickly from one person to the other -- that could make you look untrustworthy. Make eye contact and hold it for 5 to 10 seconds. Then do the same with the next person. If you are presenting to a larger group, pick a half dozen to a dozen people in various spots throughout the audience to be your points of connection and make and hold eye contact with them. This projects confidence and makes a connection with the people in the audience. It also feeds and energizes you, which can catapult your performance to the next level.
What you do with your hands. Earlier, I described the most powerful stance is to have your hands at your sides. That doesn't mean that you stand there like a statue. Use your hands to make purposeful movements -- gestures that contribute to the story telling. And then return them to "home base," at your sides. For instance, if you break your presentation into three parts, you can hold your hand high and hold up one finger and then two and then three when describing the three parts of your presentation. If you are talking about a reduction in expenses, use your hands to describe reducing them from this level (above your head) to this level (below your waist). Make BIG movements that are out of the ordinary. I've heard this described as "letting the armpits breathe," which I love because so many presenters feel uncomfortable moving their elbows away from their sides. Big movements -- especially if they are directed AT the audience can be a way of turning what otherwise might be a fairly boring presentation into a 3-D presentation.
Most people who have not been trained tend to keep their hands in front of them as a default position. This is only natural because it is a defensive posture -- we subconsciously want to have our hands out front ready to protect us from whatever is coming. But that can literally get in the way of our connection with our audience. It also makes it likely that you will begin to wring your hands and do other distracting things. So stop that.
As you prepare for your next presentation, work a few of these tips into your preparation. Actually think about HOW you will deliver the ideas nonverbally. How will your body help you tell your story? You will find that these nonverbal techniques have the greatest impact on how you and your message are perceived.