It does help to be extraverted, but I'm the opposite and had a fair bit of success debating back in my school years. You don't have to be an "argumentative person". In fact that usually works against you. The idea is to present a rational, well thought-out perspective on your topic, then pick up on any flaws you see in your opponent's logic. If you get too emotional, you'll lose your stream of thought and possibly give your opponent a chance to spot a weakness in your side. And it gives you the same opportunity, if your opponent gets too excited.