If you can throw yourself on the floor it is not too hard to writhe to the edge of the stage. If you lean on your guitarist during a solo, you won't be embarrassed to rest your head on her shoulder. On the other hand, you must also select from all the options the ones that best express your concept and throw out the rest. Or then again, you might. Once you open the door the possibilities are endless.
Spontaneity is a crucial part of a vital stage show.
Although I've mostly been talking about very broad gestures that a rock band might use, the ability to respond in a moment to whatever stimulus presents itself is essential for every style of artist. One of the most moving performances I've seen was a very simple and genuine concert by James Taylor. I don't know how much he needs to practice his story telling now that he's done it for so many years, but I'm sure there was a time when he had to structure it without making it sound or feel stiff. Yet there was always room in the structure for him to respond to what was happening around him. Whatever your personal style, whether it's wild or sedate, fun-loving or serious, you need to be genuinely affected by our material and it has to show.