Jarvan received several buffs recently to his E and W, making him a viable pick in the jungle again, and his winrate is currently among the highest.

Pros: + Mobie + High burst damage + Strong ganks and influence throughout the entire game + Strong early dueling power

Cons: + EQ combo is easy to dodge + Your ult can mess your teammates' kiting

Black Cleaver
- A very well-rounded item that J4 can make full use of, from the stats to the passives -> priority rush.

Dead Man's Plate
- Very useful against AD, help make faster rotation and stick better to target that can kite.

Maw of Malmortius
- Really strong against AP assassins as well as AP champs in generally with the passive.

Locket of the Iron Solari
- Strong for teamfights against AOE ap, very useful stats.

Ravenous Hydra/ Titanic Hydra
- Give you better clear and a bit of extra burst, as well as some AOE dmg in team fight, get this item if you're fed.

Guardian Angel
- A really solid item at only 2,4k gold, buy time to wait for your skills to go off cd and your teammates to help.

Spirit Visage
- Apart from the healing passive, which is only useful when you have a lot of lifesteals or have a soraka/sona, this item regardless gives really good stats.

Yomuu's Ghostblade
- Get this item if you want to assassinate some squishy targets.

1. Gank the lane that wants to fight, because they'll both be low and a gank or 2 can swing the lane hard.
2. Prepare for the scenario that their jungler show ups for a counter, retreat if you're uncertain that'll you will win 2v2 or 3v3.
3. Always look at the mini-map and mind the position of other lanes 30s or so before a gank to make decision.
4. Prioritize lanes that can give you easy kill first (over extending, low mobility, squishy, strong match-ups, .etc), and abuse that lane to get fed, then snowball the advantage to other lanes.
5. Keep track of enemy's flash cd and visit that lane as much as possible during that time frame, since your ult is a 3.5s lock up if enemy doesn't have dash.
5. Ward surrounding whenever convenient.

When there isn't really any easy ganks:

- If your bot is losing, get good vision control then sneak a dragon when their bot recall.
- If your bot is winning, gank bot, then get the dragon.
- Towers are also important, taking down towers give a lot global gold and map control, without the turrets, your laners will more likely to roam to help you with ganks while your enemy will be less likely to do so. Therefore, go to lane, drop your flag and start smash the turrets whenever you're free to do so, remember to put the flag behind so you can Q to it should anything happens.
- When your fed bot or top is winning hard and overextending, start invading the enemy's jungle and litter it with wards, doing that will starve the enemy jungler's from farm while keeping your fed lane safe, ensuring that they keep their lead. Having good vision control will also allow you to dive turret with your fed lane without consequences. Leaving them alone, farming your jungle, allowing them to get ganked because of their overextending, trying to make use of their lead generally will cost you the game.

Depend in the situation and how fed you, your teammates and your opponent are to make your decision. J4 can dive, assassinate, peel, split, flank quite effectively. Normally, you want to combo squishy targets and obliterate them instantly. However, that's not always possible.
If your carries are fed, you should peel for them, trap the divers inside your ult, and fight them there or EQ out if you're not tanky.
If your team has a huge lead and you're fairly tanky, you'll want to force fight whenever your team is grouped.
If you're the only that is fed, you may want to split and take towers and ask your teammates to wave clear and stay behind turrets, J4 has decent dmg is quite slippery while being a decent 1v1 fighter for that purpose.
If they have only one really fed carry, while other are just plain useless, you can op to dive that target, itemize against them in advance and make sure your path doesn't have vision before diving in however.

+Learn to use smart cast if you haven't familiar with it, it is extremely important that you use your combo as fast as possible to leave the enemy least time to react.

+Always be efficient if you want to carry: always do something useful, either farm or gank, always have a purpose with calculation in mind, don't mindlessly running around the map. Usually, the easiest way to be efficient is farm a camp when you have smite, gank nearby lane if possibe, then go back for another camp when smite is up again, ward in the process when convenient. Much later in the games, you can off for split pushing if no important objective is there to contest, to pressure lanes.

+Remember to always ping on my way in advance of a gank and make sure your teammate see the ping( ping right next to their champ), I saw several junglers don't ping or ping way too far from their teammates, and then dive in alone to give the enemy free buffs.

+Try your best not to die early, especially when you have buffs. Dying early as a jungler is going to put a huge burden on your teammates and lose a lot of map pressure, it is even worse if the enemy got your buffs. Therefore, when the enemy's jungler show up for a counter gank and you are chunked, disengage while look for opportunities to go back in. Ward the river in the beginning of the game, before taking your first buff, this period of time is the time that you're most vulnerable to invade.

+You may want to ask your team to group up early to siege tower, not only that the towers are easier to take down early, but also that the enemy's carry are not as strong, therefore, you are a lot more dominant during this phase.

There are a few mechanics tip that you can make use of, practice them when you have time, :
Flash knock-up, use to extends the range of your EQ combo and to knock up more carries in fights. This combo, however, does not do damage. By Aminizles Play Video
Also check out this video about flash combo from MachinimaRealm, j4 flash combo starts at 1:00 Play Video
Double Q on a flag, the timing to use the EQ combo is also flawless. By Icemanrai Play Video

+If you're caught by several enemies, ult to trap them in then EQ out to run away. Try to combo over wall whenever possible, you create much more distant and is likely out of the enemy's sight when jumping over a wall.

+Put your flag behind or over a wall when taking a tower, it allows you to escape when the enemies show up while having the attack speed boost, also give vision. Special thanks to binhduong

+Learn the distance of your Q( 770 range) and E( 830 range), this small 60 range difference usually makes you miss your combo if you just drag your mouse as far as you can to put the flag down. Special thanks to Mezie Emelle

+Go for your bottom side buff first, start with the double Krugs or Gromp because of the better leash. Special thanks to Diamondskin

Q:Have you ever built triforce on him?

A: I occasionally do. Trinity force is a situational item on J4 if you want a midgame power spike and is really ahead, and want to close out the game during this phase. It's a decent item to take down towers or burst down a target in one combo. However, if the games drags on to late game, tf is a lot less effective and is not very gold efficient as Jarvan's kit can't make use of many things that tf has to offer.

Q:What's your opinion on an early sightstone on j4?

A:It's a decent pick if your lanes are winning matchups and are pushing high, especially 2 solo lanes. Ward deep in the enemy's jungle and prepare for counter ganks, counter jungles. However, if solo lanes are even, it's really not a good idea since an early 800 gold is quite a lot, you can gank much easier if that money is invested in early dmg. also, the chances that you lose a 2v2 when the enemy's jungler shows up is lower. Moreover, later on, sightstone is not slot efficient and you will eventually have to sale it for something else. If you do decide to build a sightstone, try to finish your jungle item and get a boot first, the sightstone only make sense if you already have at least those 2 items.

Special thanks to Ryan Bandilla for the questions.

So, that's it. That was my guide on how to carry from jg with J4. It's now your time to bring them into practice.
I'll try my best to upload my games later to give you an idea when i have time. In the meantime, Keep playing because only practice make perfect.
Feel free to leave any comments or questions, i will try to reply them as soon as possible.
Thanks for reading, sorry for my bad English.