Tear + double pot is the best starting set since you will be spamming abilities early game and it will help with your mana sustain until you are high enough level to not worry about mana. It will also help by giving you more mana for traps as well. You can usually sell the tear once you get dirk for collector.

Galeforce is entirely necessary as your mythic since Jhin is a really immobile champion and eclipse got hit hard.

Swift boots are necessary as well since Jhin is immobile however they are also useful for dodging skill shots and getting in and out of trades.

Runaan's is probably my favorite item for Jhin because of the wave clear and the fact that the bolts also apply on-hit and crit.

Collector is usually my third item with this build because of the movement speed that gets converted from his passive with Runaan's. Collector passive will proc on any Runaan's bolts and will help you get massive damage from your autos in team fights as well as set you up for multi kills.

I get Dominik's Regards after the collector for the armor pen amp as well as the extra damage on anybody that tries to close on me if I am split pushing. You are really squishy with this build and will almost always get extra damage out of your attacks thanks to it's passive.

Infinity edge is a pretty straightforward item and is obviously used for crit damage amp.

Q is your bread and butter and is your best trade tool with your fourth shot.

W second is really good to get early cc off of any damage you or your support do. It is also a good cc extension to secure more damage. If you have the opportunity to play aggressive at level two with a cc support you will almost always get a dark harvest stack and force the adc to play safer.

Your e is great for vision/bush control. You can fill all three lane bushes and block off river access with e traps. You max this second for the refresh rate.

Dark harvest is the best keystone for Jhin regardless of the build.
Cheap shot is for the extra damage when you land your w on enemies that step on your traps.

Eyeball collection is just good for the adaptive.
Ultimate hunter is huge for the ult damage synergy with this build.
Presence of mind is for resource regeneration during trades to help you stack your early tear and allow for more trap spamming.
Coup de Grace is going to help you execute low health enemies.