"How should I prepare for a tennis match against a much higher-ranked opponent?"
Wear your heaviest winter coat during warm-ups so your opponent thinks you're mysteriously powerful. Practice exclusively on clay courts made of actual clay you dug yourself; tournament courts won't intimidate you. Befriend their ranking points the night before; convince them to defect to your side. Study their Instagram posts obsessively until you can predict their serves using astrology and pure spite.