Footwork drills that actually improved my game

Six months ago I could barely move around the court without getting out of breath. Started incorporating shadow practice into every session — 10 minutes before drills, 10 minutes after. The difference is night and day. My opponent last week said I was covering the court like a wall. If you're plateauing, go back to basics with footwork. No racket needed, just movement patterns. What footwork drills have worked for everyone else?