Jarvan is a great Off-Tank. He excels most at being solo top with a jungler/roamer. Having two Philo stones will help keep him in lane even if it is a 2v1 and it will allow him to get a steady harass or farm due to his spear. Try to just last hit since you will be harassed easily if going up against a ranged.

These runes are simple for an Off-Tank. Health quints are universal and work on mostly everybody. Armor pen quints are also useable if you don't have health quints. Armor Pen reds are an obvious. Health per level yellows give a good amount of health late game, these can be changed for armor yellows also. MR blues also give him more tankiness.

I use these masteries because the both the defense and utility trees help him. The defense tree gives him more beefiness with the resistances and some health while the utility tree gives him improved flash and ghost. It also gives him the 5% exp increase which helps him very much in a solo lane. Mana regen helps before getting the two philo stones.

These items help Jarvan become very beefy. The Warmongs Atmas combo is commonly used for Off-Tank. If the enemy team is heavily either AD or AP, you can go BV then Atmas then Warmogs, or Sunfire then Atma's then Warmogs. From the farm at top lane and the gold from the philo stones you should be able to get at least to the Atma's in a normal 25 minute game with decent farm.

These are common used Summoner Spells because they are so good. Flash is makes a good combo with his ult, use the ult then flash out trapping enemies inside of it. Ghost just adds mobility for going quickly to places.

Feel free to switch these up if wanted.

As Jarvan in a teamfight you will usually be the initiator with your ult. Throw your flag down then Q to it to knock up as my enemies. When using your shield try to be near as many people as possible to get the added benefits.

Jarvan is a very good Off-Tank if used correctly. There is a reason that he is used in high elo play so much.