I just got back from 5 days in New York for Opera America Board Meetings, and along the way, I was able to hear tenor Jonas Kaufmann in recital singing Schumman, Strauss, Wagner, and Liszt - what an evening (including six encores!)
I was reminded again how a great singer can command a stage (Carnegie Hall in this case) with just his voice and a pianist. May lessons here for the auditonee. In addition to being a great singer, Mr. Kaufmann is not afraid to do nothing when it fits the occasion - there was never any empty gesticulation - every move or non-move meant something.
More than anything, when you audition, remember that it IS a performance, and your job is to not just get hired or win, but to touch and move your audience, whether its 3000 people or 1 general director.
The power of the human voice to touch us is awe inspiring - tap into that anytime you sing, and certainly don't leave it out of your audition!