Hey there,
I am an high ranked main ADC. Espacially Jhin and Vayne are my favourite Champions. Due the fact that you clicked on this guide you want to learn Jhin. That´s a good decision. In the current and following Meta he is going to be one of the strongest ADC´s and Carries in the Game. He is not banned often and there are less people who play him at all. So it´s a good Time to learn him.

Like said in the Introdcuction - he is a really strong laner. The 4th AA has a lot of damage and if played right he can carry nearly every game. He has a long CD on W in early-game. In case you want to take the biggest advantage on the lane try to get a good premate Support. More to this in the "Laning" Section.
Jhin is like nearly all ADC´s hard to master - but if you put the time and effort into him he will give you a lot of fun and LP in exchange. Do you like to count to 4? Do you like to oneshot the enemies before they even see you ? Do you like to snipe and look cool as hell? If you answered one of those Questions with "yes" then he is YOUR next Main-Champ.

Pros:

Hard snowballing
Strong Laning Phase
Outscales nearly every other ADC
Good farming
Massive powerspikes with every Finished Item

Cons:

Weak if really behind
Strong reallying on his Support to make good plays before being fed
High skill required if you want to play him in higher Elo´s
Hard lack of mobility (good working with mobility granting supps like Janna, Thresh, Lulu or Karma)
Squishy like paper

In the early game you will most of the times only stay in mid-lane and freeze it there. Farm safe, use 4th bullet for Canon Minions or to poke on the enemy laner. The first 3 shots aren´t worth to be used for poking because you need it for the minions. Wait for a gank from the jungler and let the enemies overextend. Keep the tri-bush always warded and place a deep-ward at river in front of the drake (good place for vision - sight on Drake and the pathing of the jungler). This sets the success of an enemies gank down to maybe 15% because the only option left is a lanegnak which can be really risky nn lower level.

Which Supports synergize really good with Jhin?
First and in my point of view best is Tham Kench. He gives you a good CC, can safe you and lock down dangerous enemies for 3-3.5 seconds. He got a free escape/engage with R for you and his W gets you out of every dangerous situation and helps you to dodge. Jhin´s biggest weakness are lockdown supps. So he can just eat you once your caught in CC to avoid taking damage on you. Furthermore he synergyzes perfectly with your passive. Once you shot your 4th bullet he can eat you, bring you close enough to the enemies target, spit you out and while you were in Tham you were able to reload. So actually he is the perfect bridge between attacking and reloading.
Secondary i think Lulu, thresh and Blitzcrank are really good with him. Thresh and Blitz because of the hook/pull and saving ability due to a lot of CC and Silence. Lulu is strong because of her Shield, Speedbuff and Attackspeedbuf (Both give you AD), the R for the tankyness which equalizes one of his weaknesses (squishyness) before you get the Lifesteal. The polymorph helps you to kill fed targets or to just take out a carry.

You took the first enemies turret on bot, you got like 220 CS after 20 mins and maybe 1-3 kills? Then it´s time to spread your lead on the other lanes. Check the Map at first. How are the other lanes going? Are there any objectives to take (Drake, Herald up?)? On which of the enemies you have sight and where can you walk without getting assassinated by the enemies jungler or roaming midlaner? Always ask yourself those questions. Never ask "What can i do to get myself more feed?". Rather ask "What can i do to get THE OTHER members of my team fed and their lanes ahead?". If you do this, you are going to become a better player. Having a lead is always nice - but it´s a teamgame- So always try to improve and get your teammates a good lead as well. It is way easier to win a game if you don´t have to do it solo. So to come back to our topic - what to do in mid-game? You mostly like to go to the drake with jungler and supp and take it as fast as possible. Ask your supp if he can check if the enemies have vision around it first. You can avoid to get it stolen if they got no vision. After it check if you can pick someone off-guard together with jungler and Supp. In best-case you can take someone out and push as 4 the mid-lane turret while Top is pushing as well. Always keep a good pressure on the map so the enemies can´t do what they want.

Look which lane is going good. Try to go with the strong members of your team and get some CS while getting a good protection by them. Try to get turrets done, get farm around the map, never go alone to avoid getting assassinated. In case you aren´t ahead you WANT to live and don´t give any kills to the enemies. When you get farm you can catch up - but if you die for it the enemeis lead will get bigger and bigger.

Now it´s time to shine as the brightest.
You got your Items ready, you got some turrets down and your team is ready for a teamfight. Group up and set your CC spells on the enemies strongest carries. You can take them out with 3 AA´s, Q, 4th AA. If you see that your team is having CC on a strong champ just use your W to follow-up the CC without giving them the possibility to dodge it. If the fight is going good and the enemies try to escape your team use your R from a safe position with vision around it (or protection by your supp/tank). Shoot your bullets on the targets you are sure to hit. Even if the damage can´t kill some of them the slow will be hard enough for your team to follow up and execute them. Take as many turrets (or inhibs) as you can before going back. Once you got down anything you can get before the enemies respawn you can still do another drake, elderdrake or even baron because the pushed minionwaves on the lanes get the pressure on them. They can´t defend and contest your team at the same time.

Jhin is a really strong champion and a lot of fun to play. If done right you can win so many games just by following this guide. If you have any questions left just go ahead and ask - i will check the comments/massages daily. Good luck in the rift and always think :"How can I improve as a player and help my team?" - with this words, until my next guide.
Post Scriptum:
The next Guide will be a Vayne Top/ADC Guide. I will keep all of my guides updated once a new Patch comes out. If you want to learn Yasuo check out my Yasuo-Guide :
https://www.mobafire.com/league-of-legends/build/yasuo-7-23-mid-top-total-dominaton-guide-517103

If you´d like to keep up with the great support your doing for me then check out my new monster hunter world youtube channel as well, have a great day and good luck on the fields of justice :)I´d be glad about any kind of support.

Link:
https://www.youtube.com/channel/UCoKCr-hcDh6K0yikPwLtxsQ