Personally, I dont farm as much in jungle as alot of others. Considering Jarvan's ganking ability, Applying pressure to the lanes as much as possible is crucial. Even if you dont go for a kill, Showing some presence in the lane can push them out and give your team some un-contested CS farm.
Blue side - Wolves > SMITELESS blue > Red > Gank bot/Apply pressure > Gank Mid > Clear through your jungle then head back and grab your razor and boots if you have enough. Possibly some pots and wards.
Purple - Wolves > Smiteless Blue > Red. Now depending on the top lane enemy, You can either go straight top and gank or gank mid, Counter jungle the wraiths then head bot through their jungle and gank via Tri bush.
Winning mid to late game rests on your shoulders.
A decent J4 initiation can dismantle a team in seconds, Bide your time as much as possible so you can get your hands on their AP or AD carry.
If the other team decides to engage on you first, Peel as hard as you can for your carry's. The moment the enemy carry is within range for your team to switch and melt their face.
If your team is able to get to the enemy carry, the best thing for you to do is split their defence. E-Q onto someone that is between the carry and their team and ulti to split them up, That way, it will force them to burn their flash and or an escape move to get out. That way, by the time the fight is over, they have nothing to disengage and retreat with and will normally result in more kills or an ace.
A decent intiation can also waste ulti's or high CD skills, For example: If you can get ontop of a Sona, Make her panic and waste her ulti on one person. If your team is not in a decent position, You can disengage, regroup and go in again. With Sona's ulti will be down and result in a better result for you.