It finally came to me watching a video of myself doing some storytelling on stage, in front of an audience. See, I'm pretty comfortable on stage, so I was really surprised to see how nervous I looked. For a while I couldn't tell what it was, then I realized: my arms were dangling limply from my sides, and I was just standing there. I knew I felt at ease inside, but standing there like a doorpost communicated nothing with my body. Os stage it's just bad, but in person it communicates self-consciousness. You see, when we communicate we don't just do it through or words, we do it through our whole physicality and our gestures, and if you're not using that to you advantage, it's working against you.
Common wisdom says you shouldn't use "defensive" gestures that look like you're covering your chest of face (ie: arms crossed, holding a drink in front of you, etc). And that's pretty true.
They also go on to say you should never "hide" your hands behind your back or in your pockets, and that's OK--provided you do something with them. DON'T just dangle your arms like sausages from you shoulders. It looks awful, and doesn't work well for anybody.
There's also a ban on hands in pockets, but I don't understand that at all. Arms hanging limply they convey a kind of denseness. I wouldn't leave my hands in my pockets for too long, and don't play with things in your pockets, cause that just looks weird, but when your hands are out of sight they're just not communicating anything. In certain situations, hands-in-pockets conveys a certain sophistication. It's a gesture that goes well with an expensive suit, for example. There's the famous "lawyers stance"--one hand in the pocket, the other raised, palm-up, to make a point.
When you're talking to someone, or a group, it's good to keep your hands up at least at elbow level. You're still keeping your chest and face open, but you're putting your hands inside the other person's field of view--of course you have to move them or you look like a zombie!
No matter how good your verbal conversation, your body may betray you if it's not in agreement with what you're saying.
Remember that your hand gestures amplify whatever you're communicating. Why not use that to your advantage? Different people are comfortable with different levels of physicality, so you have to find the degree that feels right to you.
Use hand gestures to reinforce the things you're talking about. There are so many ways to gesticulate, that I couldn't even to make suggestions. Just relax and go with what you feel. Watch how other people use their gestures to communicate, watch standup comics or public speakers.
Give it a try and post your results!