Jarvan is a secondary tank fighter who can play jungle,top or tanky support. He can be very aggressive mid/end game also can gank well and can secure kills very easily.I play Jarvan jungle because if i use my build as shown i can help my team and op with blue and red buff.

Jarvan is a good jungler when i comes to gank he can use demacian standards (E) and then dragon strike (Q) to engage and enemy/jungle and if you use golden aegis (W) you can slow them long enough to throw a few auto attacks and then finish with cataclysm (R) to finish off your opponent (not jungle mobs.) When jungling Javan can get MANA hungry so i would advise to take blue first and when you feel ready take red.

If you play Jarvan lane not jungle you need to try not to use as much mana as you can because if you use up all you mana you will have to recall/use a mana poison. If you use demacian standards (E) your auto attacks would do more damage and quicker attack speed plus if you are in trouble and it is still there you can use dragon strike (Q) to get away.

Jarvan is good with team work apart from the fact if you use cataclysm (R) you can trap you team mates in it too and if you near a turret and use it they can get trapped too. If you have finished your opponent with cataclysm (R) you can press R to destroy it. Also if your enemy flashes out of your cataclysm you can press R and destroy it. Try at the beginning (lvl 1) to make you enemy flash because it will help when using cataclysm (R).

with Jarvan you can have alot of spells for him like:
flash: it would be good if low health, lane or jungle
ignite: use in lane if your enemy runs into turret range
smite: if jungling and need a bit of extra damage
exhaust: to slow down you enemy for auto attacks etc...
heal: if jungling, lane, support or in a team fight and you or team mate has low health it can be used then
clarity: if you have mana problems with Jarvan use it for the extra mana

this is my build for Jarvan i hope you have enjoyed it please feel free to leave a comment and if you use this guide tell me how you got on good luck :) thank you for reading

p.s any thing you thing i could of added or missed out please add in the comments.