Jarvan IV is traditionally played as a tanky dps in top lane. He can dominate most enemies up there, but his ganking potential is often overlooked. By taking him to the jungle, this potential can be fully utilized to terrorize the enemy team. With his Demacian Standard and Golden Aegis, he can clear surprisingly quickly and maintain his health as he does it.

Marks

Greater Mark of Attack Damage: These are aimed towards improving jungle clears as the creeps don't have much armor and Jarvan IV's Demacian Standard gives him both passive and active attack speed.

Alternatives

Greater Mark of Attack Speed: This will improve jungle clears as well, but due to Jarvan IV's passive bonus, it may be a little overzealous.
Greater Mark of Desolation: This is more geared towards your actual ganking, as your Dragon Strike shreds armor. Going this route will most likely having you deal near true damage early game.

Seals

Greater Seal of Resiliance: This is a pretty standard rune choice for all junglers. Having the extra armor early helps to ensure you actually have enough health to gank after a clear. Jarvan IV's Demacian Standard gives him passive armor as well, but the more you have, the better.

Alternatives

Greater Seal of Defense: Jarvan IV's Demacian Standard gives him enough armor to get away with a set of Armor per Level seals; so if you want a little extra armor end game, this is a nice alternative.

Glyphs

Greater Glyph of Magic Resist: The main reason for these is so you won't need to make a larger investment in Magic Resist Items. Jarvan IV is best suited as an initiator, so he needs to be able to take a hit from any source.

Alternatives

Greater Glyph of Scaling Magic Resist: Generally speaking, there isn't going to be a huge threat from Casters early, so feel free to take these if you want to be a little tankier endgame.
Greater Glyph of Replenishment: If you plan on ganking more than normal, these might be a good idea, because Jarvan IV burns through mana quickly due to his low base regen rate.

Quintessences

Greater Quintessence of Movement Speed: Jarvan IV is the first man in and last man out. You need to be faster than everyone on the enemy team so you can catch the runners and escape the chasers.

Alternatives

Greater Quintessence of Attack Damage: If you want that little extra punch, these aren't a bad choice. That being said, you're gonna be a bit slow.
Greater Quintessence of Endurance: If you feel that you need to be a bit more tanky, these make a nice alternative because they are scaling runes in disguise.

The Masteries are pretty strait forward. Take all the masteries on the left side of the assault tree for maximum damage output. However, take Demolitionist instead of Lethality , as a 10 damage bonus to towers is good for an attack speed build, not to mention the fact that you aren't going to be getting any critical strikes, so bonus damage there isn't useful.

As for the defense tree, you want to take armor, health regen, and the Bladed Armor progression. These are aimed at getting the fastest and safest jungle route.

I encourage you to experiment with these as needed to improve your clears and according to your play style.

Initial Items

You should start your build with Cloth Armor and 5 Health Potions. This is the standard for junglers as it allows you to stay out as long as possible farming and ganking.

First Back

When you get at least 700 gold, you can go back for your Madred's Razors. If you have enough potions left, I recommend staying out until you have 1050 gold so you can get boots as well. hopefully you will have some excess gold to buy more Health Potions as that is going to be your limit to how long you can remain out.

Early to Mid Game

After you've farmed yourself up a fair amount of gold, your primary goal should be to complete your Wriggle's Lantern so you can stop buying potions. You should then prioritize getting Mercury's Treads and a Recurve Bow so you can tank the growing threat from the casters, as well as deal some of your own damage. Your first Recurve Bow is going to go into a Wit's End. This is a great mid game item because of the on hit damage and the extra magic resist to ensure the casters can't burst you. At this point, you should work on getting a Warden's Mail to help dive towers and hinder attacks.

Late Game

At this point, you've established yourself as an imposing figure in the eyes of the enemy and you need to continue imposing that fear. Build a Madred's Bloodrazor to fully utilize the power of your Demacian Standard and your bows. If the game has gone this long, then you should upgrade your Warden's Mail into a Randuin's Omen to supplement Golden Aegis. A closing item is of course the final Recurve Bow item, an Ionic Spark. This will proc about once every 2 seconds and will make your Madred's Bloodrazor even more deadly.

Note, if at any point you are having problems catching people, consider replacing the Ionic Spark with a Frozen Mallet and building the phage component early. Completing the full item early isn't as important because you have so much attack speed, the phage will likely proc before the slow from Golden Aegis ends.

Standard Route

Jarvan IV can follow several routes, but I like to take it slow, with a level 3 gank after a double buff clear.
Start at the wolves by throwing your Demacian Standard onto them and have the usual aid from mid/side lane. From there, you should make your way over to blue buff with a pull from mid and a Smite to finish it. You can solo it if you have to, but this will save you a potion. Next you should clear the wraiths and move on to red buff. Soloing red buff should be fairly strait forward with Smite coming off cooldown when it is about half dead. From here, you should go try to gank a lane. Afterwards you should clear the jungle of any creeps that respawn ganking as needed till you either run out of potions or have at least 1050 gold.

Alternate Route

For those of you interested in a route that gets you to ganking faster, you can start by killing wraiths with aid from mid and moving on to red buff with a pull from mid. This pull is strongly recommended because you want to save plenty of potions and have as much health as possible so you can gank immediately after killing it. From there, if you have at least half your health left, you should be able to take blue buff. Mid may ask for it, but you need it more at this point for experience and gold, so don't give it up. At this point, you should go back to the standard clear, ganking as needed.

The key to a successful gank from Jarvan IV is swift action. I highly recomend that you smart cast if you want to ensure that you land your knockup.

Basic Tactics

The key part of ganking as Jarvan IV is landing his Demacian Standard in the path of the retreating enemies forcing then to Flash over it or get knocked up by the follow up from Dragon Strike. The best way to guarantee you have the chance to do this is to come from as far behind them as possible. Assuming you land this combo, you should activate Golden Aegis to slow your target. You should never stand around waiting for a gank. If none are possible, then you should go back to clearing your jungle.

Tower Diving

As Jarvan IV, you have the natural ability to dive towers. The best way to do this is to lead with Demacian Standard regardless of whether you intend to use your Dragon Strike. The reason for this is that it will double your passive armor bonus allowing you to tank it for longer. When diving, you always want to use a pincer tactic with your teammates to ensure the enemy can't escape.

When you think of Jarvan IV, what the first thing that comes to mind? For me, its a shout, a leap, and an arena bursting out of the ground where you're are beaten mercilessly.

When to Use Cataclysm

The key to using Cataclysm is patience. Just because you can, doesn't mean you should. There is no point to using Cataclysm if you can't be sure the enemy will be trapped. If you know the enemy's Flash and/or blinks are all on cooldown, then ult away, assuming you know you can kill them. You can bait a Flash fairly easily using your knockup combo, just to ult them afterwards. You can also use Cataclysm defensively. If you lead with Cataclysm, you can then use your Demacian Standard, Dragon Strike combo to trap them there. This will give you about a 2 second delay before the enemy can resume chasing.

When Not to Use Cataclysm

If you know the opponent has an escape spell up, then its probably a waste. However, just because your opponent can't run, doesn't mean you should go in. For instance, never trap your half dead carry in with anyone. That's just asking for trouble. Also, its probably not a good idea to trap the enemy team's carry in your ult with your teams other melees getting shot at and not being able to do anything about it.