While this was not during workplace but during my years of college i used to feel the same way.
Generally, issues related to personality, body language, having a good public presence and charm are all linked to something within. I used attend the classes for that, but i think with a special touch from the teacher eventually it turned out this has nothing to do with my language understanding or there wasn't any formula for it.
Through my own experience and the others i have seen, essentially, it boils down to two things:
Once you really has self confidence to face people, accept and respond to what is being told - you slowly realize that your body comes to rhythm; you don't fear to express yourself, to tell truth and you are not conscious and hold back yourself while you are speaking.
Tip: have a close friend whom you can trust and keep talking to him/her. Expressing them you would feel much easy and while they should be critical, they should look from your point of view, you will begin to gain the confidence.
2. Clarity of thought:
There are others who doesn't really lack confidence, but while they are saying something several threads in their mind go on. The way they present themselves becomes like a spaghetti to reverse. This eventually leads to being upset about not being able to communicate.
Tip: Rehearse and rehearse before every important meeting, talk and try to write down stuff. This allows you to look at yourself as the other person and slowly you will improve upon how you express yourself.
In all, all aspects of personal skills always get more by practice rather than learning some theory about it. Find a buddy whom you think has got it all, and whom you can trust. And keep constant communication to him/her they can guide you how to improve in those small but important things.