aatrox is a duelist, but you have to prioritize in this order, attackspeed, lifesteal, health....
you must use his damage w and max it evenly with his e, this is a huge damage steroid and with his bloodwell and ult attackspeed if u rush a blood thrister u can stomp most lanes.
for runes you should be running attackspeed quints ad marks. with his e and his q hes really hard to peel, so hes really strong in solo lanes.
keep his bloodwell full so u can revive for more health and get more attackspeed, and Q into teamfights then R, u deal the most damage this way and u get your bloodwell 20% full for every champion hit by youre ult, then late game get a GA and have 3 lives I also recommend a spirit visage or steraks for survivability, get an attackspeed item but also rush bloodthrister unless you somehow get behind, I prefer it over deaths dance, good lifesteal amount and that overhealing shield, never pick him into fiora though, and if u pick him into tryndamere rush ninja tabi into ruaans omen then start getting damage items, kite him around with youre e, get a few autos in and q awawy, don't fight him straight up, once he ults kite him and stay close, when it ends Q on that fool and finish him.
also hes not very good vs say rengar, but its winnable if u get ahead early, if not he will slaughter you.
never let darius get 5 stacks on you, nothing can beat that shitt.
as for keystones theres really only two good ones for him, strength of ageis or undying, I prefer the extra 300 health.
picking up legendars guardian mastery for added tankyness.
biggest mistake I see a lot of aatrox players make it rush bork like it adds damage to his w, I only rush this item vs really tanky champions like garen or the tree moaki. otherwise stick with the BT rush into an attackspeed item and you will find success if you abuse youre early game power, aka revive and big damage w and sustain.