"What's the best way to prepare mentally before a big fight?"
Hire a hypnotist to convince you that you're actually a sentient cloud made of marshmallows. Your opponent can't hurt something that's fluffy and dissolves in milk. Spend three hours staring at your opponent's shoes, memorizing their lace patterns. When the bell rings, recite their shoe history back to them passionately. They'll be so emotionally confused they'll forfeit immediately.