Jarvan IV is a "DPS Tank" champion, and a very good one at that. I like to build him with HP, armor and some nice armor penetration/health-based damage items. Any items/order are situational, and can be changed according to the team comp you are facing or any other reasons you may have. This is my first build, and please feel free to leave constructive criticism after you try this build.

MY NEW BUILD IS HERE: Jarvan IV: Demacian Bad-***

Pros:
- Good initiator
- Can be VERY tanky late game, while putting out acceptable damage
- Great at targeting squishy champs with his Ult; stellar in team fights
- E+Q can be used as a nice escape mechanism
- He has a Commando skin... Need I say more? :)

Cons:
- Not the most powerful DPS champ
- Ult can work against him if not properly utilized

I like to have the following runes:

Marks: Greater Mark of Desolation
Seals: Greater Seal of Resilience
Glyphs: Greater Glyph of Focus
Quintessences: Greater Quintessence of Desolation

Again, these may be changed for certain reasons, such as jungling, etc.

I like to use a 21-1-8 build, as shown above. Sunder is important for Jarvan. I also like to put one in hardiness, just because :D. Since he lanes so well (E), I like to have Awareness as well, for the boosted experience. These can ALSO be changed, so be aware that this is not an END-ALL mastery list.

E and Q are important, especially E early game. This will allow you to gain armor and attack speed as well as harass with Q. The added bonus is you get to do your beautiful E+Q knockup combo, which is great for ganking and all-around harassment. (Useful for jungling, too)

W isn't that important, but I do like to have one point in pretty early for the added protection just in case!

I would choose Ghost and Exhaust/Cleanse. Depending on your opponents, you might need to take Cleanse over Exhaust for those nifty get-aways. I would pick Exhaust over Cleanse if you do not NEED Cleanse, though.

Ghost is just great for going into a fight AND getting out of it, so what's not to like?

This is a very good champ, and I have had a lot of fun with him. This is just my personal build that I wished to share with you guys; I am in no way saying this is the ONLY way to play him. This is just the method I have used in my previous games with Jarvan IV that seemed to work very nicely early - late game.