Hey, I'm Perpo, I've playing Jarvan IV for a long time, and i decided to make a guide here in MobaFire, so let's begin.

First you'll need Dragon Strike, in Level 1 you can deal some damange with it, then level up your Demacian Standard, now you can start to deal some damage to the enemy.

You'll need these runes.
Greater Mark of Desolation: You need this for armor penetration, your Dragon Strike will deal more damage because it counts as physical attack.
Greater Seal of Resilience: This is for armor, you can resist more damage from the minions and enemy champions, the armor will help you when you use your ultimate in two enemy champions, you can get one kill and then escape using your Demacian Standard and then Dragon Strike
Greater Glyph of Fortitude: These runes are for health, and it help you like armor, it's the same.
Greater Quintessence of Swiftness: Movement Speed.

You can start with Boots and 3 Health Potion, then buy Phage and complete the Frozen Mallet, buy a Pickaxe and then buy Last Whisper, it will help you a lot with the armor penetration. Buy Giant Belt, Chain Vest and Ruby Crystal, first you can get Atma's Impaler or if you need health Warmog's Armor, finish the build with Bloodthirster.

You'll need:
Flash: You need this to escape and enter to fight, it helps when you are on your Cataclysm and you have low health, you can flash and the enemy champion will stay in your ultimate.
Ignite: This is simple, when the enemy champion have low health, you can burn him with this.

Thank you for read this guide, this is my first guide so please, if you think my guide is good comment, and if you think it need something, comment too!

Thank you, see you in the field.