9x Greater Mark of Attack Damage
9x Greater Seal of Armor
9x Greater Glyph of Magic Resist
3x Greater Quintessence of Attack Damage

Normal standard mastery page:Defensive mastery page:

Q>W>R>E

V

V

V

In team fights, stay near your support( unless they're a diver like alistar etc) and try to stay near the back of the team, however not too far where you can get picked.
Ideally you'd want to be towards the middle of your team, safe from back picks, and non penetrating skill shots.

Dealing damage:
It's an unspoken rule that you should focus the person closest to you. There is no "set case" where you have to go for the enemy adc. That job is for your tanks and assassins. Your job as jhin is to chunk down the enemy- no matter who it is- as fast as you can.
If your team engages too quick for you to catch up, just throw down your ult and then catch up later. Otherwise it may be too late.
You can also use your ult for pressure, don't use all the shots at once, unless someones about to escape.
People in lower elo tend to panic when they see the curtain call coming out, so you can utilise that to your advantage.
Your e has a pretty big range, so place that smack down in the biggest cluster of enemies.
Use your w to catch people, and to disengage.
Always bounce your q whenever you can. It's free chain damage.
You can also use your E to disengage, because of the slow it offers.