Hecarim vs Xin Zhao

Cast Devastating Charge (E) far from your target: the longer the run, the farther the knockback and the harder the hit, and Warpath (passive) turns your bonus move speed into AD.

Cast Onslaught of Shadows (R) from range: the fear from the shockwave, at the end of the dash, lasts longer after a long run.

In teamfights, recast Rampage (Q) as soon as it's back: each cast that hits adds a stack, which lowers its cooldown and raises its damage.

Activate Spirit of Dread (W) in the middle of the enemies: you gain armor and magic resist, and heal for part of the damage you and your team deal to them.

Get out of the line of the Wind Becomes Lightning (W) thrust: it slows you and marks you as Challenged, which extends the range of Audacious Charge (E) on you.

If you have CC, use it during Three Talon Strike (Q): without his three autos, there's no knock-up, and his other cooldowns don't go down.

After Audacious Charge (E), keep your distance: it's his only dash to get back on you, and without it he has to walk up to you.

After Crescent Guard (R), don't hit him from range: for a moment, he ignores damage from outside the swept zone. Back off, or hit him from inside it.

If you survive his first minutes, play for time: Xin Zhao is strongest early on, through his ganks and skirmishes.