Killing Aatrox when his resource bar is low will make him revive with much lower health.
Attack speed reduction items/skills are great against him as most of his damage comes from auto attacking.
Try to avoid his Dark Flight’s center of impact to avoid getting knocked up.
If Aatrox builds full damage, focus him first.
Buy items with Grievous Wounds, like Executioner’s Calling, you will make him cry.
Aatrox can be extremely versatile with his W. switching between damage, or a heal, try to zone him out of attacking until his resource bar depletes. he will have much less attack speed, meaning less damage or healing from his W.