Follow this guide and you wont have to think about your Jhin setup ever again.

Champion Select
Runes
Follow the Precision/Inspiration rune page for 95% of your games. Only change between Coup de Grace/Takedown and Armor/MR/HP depending on the situation. Coup de Grace is better on Jhin when compared to other ADCs because he has a lot of execute damage built in. Takedown is really good right now though because of the tank meta. Go for the scaling Precision/Sorcery rune page if you're playing vs champions like Jinx, Kog'maw, Vayne etc. You don't need the extra sustain you get from biscuits to beat them in lane.

Summoner spells
The second decision to make in champ select. Take heal when none of the other options fit, which will be about 50% of games. Take exhaust vs ADCs like Draven, Samira, Kalista, Nilah, Tristana, Twitch etc. Or if the enemy has divers/assassins in the solo lanes or jungle for example Zed, Camille, Katarina etc. which will be about 25% of games. Even if you don't need it for lane you might need it for team fights. Take cleanse against heavy CC champions like Ashe, Leona, Nautlius, Thresh, Morgana, Pantheon, Caitlyn etc. which will be about 10% of games If you know you're gonna buy QSS later on, VS Skarner for example, you might not always need cleanse in lane. You'll just have to be careful until you get the QSS which can counter all CC. Take ghost against scaling champions like Jinx, Kog'Maw, Vayne etc. and if you know you're gonna win the lane without one of the other stronger early game summoner spells. That will be about 5% of games, especially for solo queue, there will always be fighting and you'll get way more value out of the other options.

Loading screen
Skill order
The next decisions will be made in-game, but you can still plan ahead and decide what you will be doing in loading screen. It helps with being able to focus more on actually playing the game. As a rule of thumb, Level your abilites in this order R/Q/W/E. There are some exceptions though. If you are invading lvl 1 W is better than Q. Wait with unlocking any ability until you know for sure though. There are also some situations where putting two points in Q is better than unlocking E at lvl 3. If you are not worried about being ganked and if the enemy are not divers (Champions like Leona, Rell, Tristana, Samira etc) then E is pretty useless. The extra damage from rank 2 Q is better.

Items
Item 1 will ALWAYS be Galeforce.
Item 2 will be boots, but they can be bought earlier or later, it depends on how much gold you recall with. Buy them when it fits, but dont wait too long. Atleast try to get the basic 300 gold boots on first or second back. Boots of Swiftness will be the best option for about 70% of games, but if the enemy is majority AD/AP or if they have an assassin like Zed, Talon, Fizz, Katarina etc, go for Plated Steelcaps or Mercury's Treads.
Item 3 will be one out of The Collector, LDR, Stormrazor and RFC. Take The Collector when the enemy is squishy, and LDR if they are tanky. LDR is the best option in most games, especially because its a tank meta. If you are unsure which one to take, or if the enemy is mixed squishy and tanky, Stormrazor is a very underrated item. It's a cheap way to get the 60% needed for your IE powerspike, and it also doesn't lack damage like RFC does. Take RFC only when it will be very hard for you to walk up and auto. Think Sylas, Xin Zhao, Akali, Caitlyn, Lux. The damage you get from going one of the other 3 options won't be worth it if you can't even auto.
Item 4 will ALWAYS be Infinity Edge. Jhin and IE go hand in hand and have done so forever. Do not delay you IE power spike for another item, it's never worth it. Basically, Jhin technically has an 70% Crit chance when he completes IE where as other ADCs only have 60%. It's because 25% of Jhin's autos are already guaranteed to be Crits. Of the remaining 75% autos, 60% of THOSE autos will be Crits. Which is 45% of his total autos. 25%+45?=70%. Sorry for boring you out but atleast now you will buy correctly :) But even without this IE is too good to delay. The power of IE is the main reason to why cheap item like RFC and Phantom Dancer are so good on certain champions.
Item 5 can be one of BT, LDR, Stormrazor, RFC, QSS, GA, Maw or Chainsword. Lets go through the options. Bloodthirster is essential if the enemy has a lot of poke like Zoe, Varus, Xerath, Lux etc. It can also be good in long fights vs tanky or healing champions like Ornn, Aatrox, Fiora etc. Usually LDR will be more important if you haven't bought it yet though, which is why BT is more commonly bought 6th. RFC and Stormrazor will almost never be the best options for fifth and sixth item unless you don't need any of the other options. It's a cheap way to get your crit up to 80% and 100% fast. QSS is also very situational, take it vs Mordekaiser, Malzahar and Skarner or if you forgot to take cleanse and the enemy have a lot of cc. The QSS component can be bought earlier if needed. GA and Maw are both generally good items, but are the best options if the enemy actually has a lot of AD/AP threats, or if a Zed, Talon, Katarina etc. keeps jumping on you. Lastly and most definitely least, Chempunk Chainsword. The Marksman anti-heal item, Mortal Reminder, is the worst out of all of them, especially on Jhin. It's to the point where the bruiser anti-heal item is better on Jhin. Atleast you'll be able to proc the increased grevious wounds effect more. But if you have to buy anti-heal on Jhin then your team has already let you down massively. It should not happen and if it does, you're probably loosing anyway. JK. Not really.
Item 6 is the same as Item 5, only some items are a bit better. Like mentioned, BT and LDR are usually better options for your sixth item than the likes of RFC and Stormrazor.
Late game upgrades: If the game is going to really late game, there are some upgrades you can do with all the extra gold. Firstly you should buy Elixir of Wrath/Elixir of Iron depending on what you need. Usually Elixir of Wrath is better but VS assassins and divers Elixir of Iron helps you survive the crucial last fights. Replacing items like The Collector, RFC, Stormrazor and GA/Maw (if on cooldown) for more expensive late game items like LDR and Bloodthirster is also a good move. Lastly, switch out Boots of Swiftness for Berserker's Greaves. Attack speed scales lineary with Crit on Jhin, since he gets a speed boost whenever he Crits, And in my experience Berserker's are better when you have 4 Crit items or more. But don't sell your boots completely. Don't you dare.