You must never be satisfied with losing. You must get angry, terribly angry, about losing. But the mark of the good loser is that he takes his anger out on himself and not his victorious opponents or on his teammates. ↗
I wish I could give you a lot of advice, based on my experience of winning political debates. But I don't have that experience. My only experience is at losing them. ↗
Never say no when a client asks for something, even if it is the moon. You can always try, and anyhow there is plenty of time afterwards to explain that it was not possible. ↗