Jarvan is a very diverse champion, i use him for jungling. most of being good with him is from having to know when to initiate a fight. if you know how to do this correctly you can win a 3v1 no problem.

Jarvan's abilities will deplete your mana extremely fast,hit blue buff first have someone in mid lane help you kill it tell them to leave at about 500 hp and then smite golem. Killing him with smite will grant you an extra 10 gold this is very useful after golem fight is over get Q and put your flag in the wolf pit and hit it with your Q, this will cause you to send them flying in the air and bringing you across the wall. you will do this to all other jungle monsters. Use smite a second time on red and then get W after killing the final golems move back up to wraiths and you are ready to gank after you recall and get your items.

Ganking with Jarvan should start at level 4, signal a teammate you are going in, place your Demecian Standard (E) close to enemy champion and then hit the standard with your Dragon Strike, this will give you extra time to attack your opponent. Let the Laner get the kill. Always.

Jarvans teamwork is mainly because of his ability as an initiator, to join or start a team fight wait until they clump up somewhat and then (E,Q) Combo into them and then immediately use your ultimate this will allow maximum focus on to the enemy team