Use your strongest single-target damage setup
Stay close enough to keep pressure on him, but avoid obvious telegraphed attacks
Dodge his heavy swings and charge attacks first
Focus on surviving the fight before maximizing damage
Save burst abilities for openings after his big attacks
Keep moving to avoid getting cornered
Use healing or defensive items before the fight if available
Upgrade damage, survivability, and cooldown reduction
Attack consistently during safe windows
Repeat until his health is depleted