MasteriesI have these masteries because it gives me health, armour and damage so i can stay in lane longer and farm better, as people know or will know now Jax is a late game carry if he is fead early and farmed well then he will punish the opponents. Also the masteries help jax a lot in fights by helping him stay in fights longer and able to tank the enemy team while doing lots of damage. I go 9 in offense so in lane i can do damage to the enemy and giving me the opportunity to kill him if played correctly it also helps me farm better.
RunesI go 9 +0.95 attack damage because it helps me farm better and it helps me damage the opponent in lane. i have flat AD marks because i don't want to be dominated early because jax is weak early on and doesn't do a lot of damage until he gets his ultimate. I go 9 +1.41 Armour seals because it helps me stay in lane longer and be able to take damage by minions if i want to freeze the lane or go in and attack the enemy by tanking minion or taking hits of the enemy. i go magic per level glyphs because it gives me an advantage late game against there AP's and i can focus a little bit more on Armour. Finally i go flat AD quintessence because i want the opportunity to kill my enemy lane and make it easier to last hit minions.
I go so i can kill my enemy easier and it helps me do damage early on when
jax is weak, however you can go this helps lower the Armour of the opponents and is better late game for jax so he can catch your opponents and kill them easier.
i also go so i can get in and out of fights it is also very useful for getting out of ganks. also flash is good so you can get to the weak people like the ADC or the AP carry and kill them quicker to help win team fights. i recommend always having this summoner spell.
Passive: Relentless Assault
Jax passive is only good if you keep the stacks up so you hit faster, jaxs other abilities help him keep hitting the enemy.
Q: Leap Strike
Jaxs Q is good because it helps close the distance with your enemy so you can keep on them in a fight, it also helps you get away fro danger by being able to jump to your minions and wards. i recomend maxing it last because it does the lease damage of all his abilities.
His W is brillent in many ways because it gives jax the ability to do a lot of damage and it also resets his attack animation (i think) so when you hit make sure you press hit straight after so you can do max damage. The cool down of it gets better the more you level it so i recomend maxing it first because it does lots of damage and you can spam it.
E: Counter Strike
E is amazing it does a large stun this fits perfectly with you Q because it jumps you into the enemy and you can stun them helping you do damage and stunning people who need to channel there ulti like kata. it also mizes good with your passive because you can keep hitting them easily and keeping the stacks up so you hit faster.
R: Grandmaster's Might
his ulti is the best part of him because every third hit he does a lot of damage so when you hit lvl 6 you are much more stronger and start to dominate. he also gets Armour and MR so he is extra tanky and can easily solo any one.
Item Buildsi choose this build because it gives you damage and you can tank the team so you can stay in fights longer. (Don't be afraid to change the build if you need to depending on your enemy team like more Magic resist if they have more then one AP or if they are fed)