As the royal family of Demacia for centuries, members of the Lightshield line have spent their lives waging war against any who opposed Demacian ethics. It is said that every Lightshield is born with anti-Noxian sentiment in his blood. Jarvan IV is no exception, even though he is the first Lightshield born to the age of League of Legends. As his forefathers had before him, he led Demacian troops into bloody engagements with Noxian forces, and on many occasions he has bled alongside wounded allies and fallen comrades. In his most crushing defeat, he was outmaneuvered and captured by a Noxian battalion under the command of Jericho Swain. This mistake nearly cost him his life at the hands of Urgot, but he was rescued by the Dauntless Vanguard, an elite Demacian strike force led by Jarvan�¢ï¿½ï¿½s childhood companion, Garen.
Those close to him believed that his capture changed him. Xin Zhao was quoted as saying: "His eyes never seemed to look at you, only through you to something he could not look away from." One day, without warning, Jarvan IV handpicked a squad of Demacian soldiers and left Demacia, vowing to find "atonement". He began by tracking and hunting the most dangerous beasts and bandits he could find in northern Valoran, but he soon tired of such prey. Seeking something that only he understood, he ventured south of the Great Barrier. He wasn�¢ï¿½ï¿½t heard from again for nearly two years. After many had assumed the worst, he returned to glorious fanfare on the streets of Demacia. His Demacian plates were adorned with the bones and scales of creatures unknown. His eyes bore the wisdom of someone twice his age. Of the twelve soldiers who had departed with him, only two returned. In a tone as cold and steady as steel, he swore to bring the enemies of Demacia to their knees.

Start of With cloth armor and 5x helth potions for dmg resistance and long duration on a lane withouth porting back(These items should be enough to get some gold).
Then proceed to Heart of gold for health, armor and awesome passive gold generate.
Now then, you may now purchase Boots of speed. But before you upgrade them to Mercury's treads, you should get another Heart of Gold.
Now when you have 2x Heart of Gold and Mercury's treads, you move on to the next item, which will be Last whisper, which grants you damage, and some awesome armor penetration.
!!IMPORTANT!!!
You might get Yomumu's ghostblade instead of Last whisper, if your enemy isn't going heavy armor!
Time to get some real damage. Atmas impaler is the solution for offtank dps!( This is, where all the hp is gonna hit ya) 2% of your max hp is converted to your Damage and you get 45 armor and some crt dmg which is kinda unneccesary but it's still worth the Unique ability :3.
It should be about Late game now, where Banshee's veil is a MUSTHAVE, so don't hasitate and get it(Not that it only gives you shield against spell, also it gives you magic resist, health, and thanks to Atmas, it will convert 2% of the health to your damage).
Now proceed to Randuin's omen(Great passive cooldown reduciton, health, armor, health regen and once again 2% will be converted to dmg).
Well you rarely get to this point, but if it happens so, then sell the last Heart of Gold and get a frozen mallet to slow down enemies, more HP and once again awesome Atmas will convert 2% of your hp to dmg. Then you should have about ~300demage.

Your most important skill will be the Demacian Standard, which you should be focusing on.
It deals demage to enemies from high distance, but also buffs yourself and your team mates.

Then there's Golden Aegis which helps you to survive in team battles. I prefer to use it even when its 2v2
NOTE:It's useless when you don't have teammates around you.

Dragon Strike isn't that great at dealing damage. But when you pull yourself to the Flag, it will knock the enemy in the air, if you pull yourself through the target, also it deals some dmg:)

And last is your ulti, which is VERRY important in team fights!

You can actually pick whatever you want.
You should always decide which spells to take depending on your Teams spells.

Pros:
Great Farmer
High survival Ability
Ulti grants you the kill by 80%
high armor
high dmg mid and late game
Great pusher
Good in Team fights

Cons:
squishy dmg early game
Mp lacks
focused verry often
Kinda hard to play
Screwed against madred bloodrazor

Jarvan is good in solo matches but even better in Premade, cuz of his Ulti, which barricades your enemies so they can't run away unless they have flash. Thanks to that ulti, your team will have an easy play, if you have ranged players.
!!IMPORTANT!!
Do not use your ultimate to KS.
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Always wait for your team to cover you. Thats when your Ultimate is neccesary. TO HAVE AN EASY KILL!Unless you suck and fed the enemy so badly, that he's unbeatable.
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If you don't have your ulti cuz you wasted it or you're not lvl 6 and your team starts to gank, you should be assisting your team by putting the flag to buff your teammates and pull yourself to the enemy, to airknock them, so they won't be able to run away.

Last hit with your Q and R spell to farm creeps, when ur laning against others.
If youre enemy is pushed back from his minions, you may last hit them with normal attacks to save MP. That's the best way you can farm creeps.
Dont worry if you miss few of them, thanks to Heart of Gold you will be gaining 5 gold every 10 secs. It might sound ridiculous, but it is REALLY Helpfull!