first thing you need to note is that this build is for you to spend a long time in the jungle and ganking and not much time in base. You will have nice sustain in the jungle.
When ganking with J4 make sure to hit the abilities. What makes a good Jarvan is hitting the E -> Q combo. This way you get the knock up and your team mate can help deal loads of dmg.
If you miss 85% of the gank is gone.
start with the hunters talisman and a refilable potion. you should farm to complete the stalkers blade and get a ward. (at least 775 gp)
With this you should be able to stick around the map and gank and farm like crazy. Help your teamates push towers and get objectives.
Finish the warriors, next go for a hydra item. after this you should get tanky. Buy magic resist or armor according to the situation in game.
You want to start with your duo lane for a safer clear. Get a leash and smite the Gromp or krugs asap. The sooner you smite que faster its up again. next move to your Red or Blue depending where you started. Get the crab early for more health. Give mid a lvl 3 gank (all you need at this point is to do some dmg and put the other mid laner on the back foot.) dont stay too long, keep farming.