This is the very first guide I have done, it will be very basic until I have to to make it all fancy like. I bought Jarvan IV today and this is the build I've found to be most effective. It is a mainly DPS build.

For runes I use :

9 X Greater Mark Of Desolation (Armor Pen)
9 X Greater Greater Seal Of Evasion (Dodge %)
9 X Greater Glyph Of Warding (Magic Resist)
2 X Greater Quint. Of Fortitude (HP)
1 X Greater Quint. of Resilience (Armor)

This rune setup allow me to be somewhat tanky, especially early game and allowing me to hit harder with the armor penetration.

For masteries I spec 21-9-0. I will upload a screenshot but its pretty self explanatory. My 9 in defensive masteries goes into magic resist, armor, and dodge.

I am not sure how to add the picture with item names and descriptiong so for now I will just put the item build and order I use.

I start with Doran's shield, save up to get Mercury Treads and Zeal. Then I get a Vampiric Scepter and begin working towards Warmogs. After Warmogs I buy a BF Sword and turn it into a bloodthirster. At this point depending on how the match is going I will either save for an infinity edge or turning my Zeal into a Phantom Dancer. .... I have to play a game now I will finish the rest later :D