Pros: Extremely tanky
Good damage
Good knockup if used right
Easy to use

Cons:
Ummmmm...........

This is my guide to how to play Jarvan successfully. I wont go into much detail, because most of you are probably just looking at the items, masteries, and runes anyways. If this build gets a decent amount of feed back, I will actually go into more detail about everything, and give it those pictures that we all love to see in guides so much.

Armor Pen Marks and Quints: Really strong overall. Makes it so you dont have to waste money on a ghostblade or last whisper to get your armor pen.

Flat Armor Seals: Armor yellows are pretty common and cheap runes. They are very nice to have for early game.

Mag Res Per Level Glyphs: Pretty much the only option for Jarvan. IMO the rest of the glyphs are borderline useless on him.

Simple breakdown:
Start with regrowth and health pot: gives you better sustainability

Next buy double philo, then boots, and then heart of gold: crazy sustainability, lets you spam skills, and they pay for themselves.

Everything after this is situational. If the enemy team has more AD then AP, go atma's first and then build the rest as you see fit. If more AP, then banshee's or FoN. Adjust to how the game is going.

Only real important fact is that you max your spear first. Once again the flag and shield are situational. If you feel that you are getting poked a lot, put points into your shield to negate that. If you are just bossing it out, put points into your flag.

Summoners: I personally like having teleport and flash. Teleport allows you to constantly be in lane and can be used to teleport gank. Flash is one of the summoners that i always get. Other reasonable choices are the following: cleanse, exhaust, and ghost. You can probably use ignite too, but I'm not a fan of running ignite unless im using it to counter champs (ie Vladimir).

1: Laning phase just farm and poke. Farm and poke, farm and poke, farm and poke, farm and poke, farm and poke, farm and poke, farm and poke. If your opponent gets out of position, then you can kill them.

2. If you flag drop and immediately spear towards it. Your spear will be off CD before the flag disappears. Meaning one flag = two knockups.

3. Use your shield's slow to not only run from enemies, but to keep a straggler slowed down for an easy team kill.

4. Utilize your passive. 10% of the targets current health on your first strike. Meaning that Jarvan pokes really hard.

5. Use your flag drop and ult to keep enemies off your carries. You don't need to get a ton of kills as Jarvan. Just disrupt the enemy team as much as possible.

There you go. A very short and simple Jarvan guide.