The best way to do well and to be confident is to be extremely well prepared. Try to anticipate all possible counter-arguments and have your counter-counter-arguments ready. You don’t have to bring them up unless you need them. Talk calmly, no need to rush. And remember that if someone is arguing against you and their arguments are foolish or unprofessional, it is sometimes better to not get drawn into the mud – better to let them hang themself. 😃

Oh, and also realize that most everyone else is probably just as nervous as you, regardless of how they might seem.