If you play Jarvan in the jungle its important to build up health early. With this you can max the use of his Combo. You can dive with your Ult, getting the towerfocus and make it easy for your teammate to land his normal autohits or spells. So you can fight under turret even with a squishy teammate. The high sustain is important in lategame teamfight when you ult 3 or more enemies. While they start to attack you you can either jump out with e and q or try to hold the Focus as Long as possible using ur w to live longer while the rest of your Team attacks from out of cataclysm.

Playing Jarvan as an AD Offtank based on supports by ganks you max first Demacian Standard. Through this your Team gains more attackspeed and armor making it especially for the ADC more easy to survive in Teamfights against other CC Teams. Max your W in the end because it isnt as effective as Jarvans other cc spells.

Because it is very hard with Jarvans low Damage in early game i take AD runes which sticks perfectly with his e passive. Building him as a resistent Tank based on Supports by gank you need to have high resistence against all Kind of enemies. His Bonus health grants him to sustain way more making him very usefull in early Teamfights.