Malzahar vs Irelia

Avoid free damage to keep Void Shift (passive) up: when you haven't taken damage or CC for a while, you take much less damage and ignore CC.

Push the wave with Malefic Visions (E): they finish off low minions, then jump to the nearest enemy when their target dies, restoring your mana.

Cast your other spells, Malefic Visions (E) included, before Void Swarm (W): each one adds a Voidling, and they go after the targets of your visions.

Save Nether Grasp (R) for the enemy carry: you lock them down while you channel, and the zone around them also damages their allies.

Don't stand near your low-health minions: Bladesurge (Q) resets when it kills, so she chains dashes from minion to minion until she reaches you.

As soon as the first blade of Flawless Duet (E) lands, change direction: the stun only hits enemies caught between the two blades.

Take your trades when Ionian Fervor (passive) isn't stacked: she builds stacks with her abilities, and at max stacks her autos deal more damage.

Save your burst for after Defiant Dance (W): while charging, she takes much less damage, but she can't do anything else.

Dodge Vanguard's Edge (R): its blades make you Unsteady, which resets Bladesurge (Q) on you, and the cage they form damages and slows anyone who crosses it.