Malzahar vs Yasuo

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.

Hit him with a cheap attack to trigger the Way of the Wanderer (passive) shield, then start the real trade: otherwise, it absorbs your best damage.

If you have projectiles, save them for after Wind Wall (W): it blocks them all for 4 seconds, on a 25 to 17 second cooldown. Other spells go through it.

Don't stand right behind your minions: each one gives him a target for Sweeping Blade (E), and he gets closer to you with every dash.

Get out of the line of his whirlwind, the third Steel Tempest (Q): without a knock-up, he can't cast Last Breath (R).

Judge his threat by his crit items more than his level: Way of the Wanderer (passive) raises his critical strike chance, so each crit item does more for him.