Darius is a dominant laner; exert early pressure, use Q for sustain and damage, and look for kill opportunities with E and Ghost.
In teamfights, avoid initiating. Instead, follow up on allied engagements to secure kills and reset your ultimate for explosive damage.
Against Darius, dodge his Q's outer edge, manage Hemorrhage stacks by maintaining distance, and kite him effectively to mitigate his melee strength.
Stats
Q
W
E
R