I tend to start off with a Sapphire Crystal, it makes it easier to spam your Q, and it builds into a sheen. The goal of laneing phase for Jarvan is to harras enemy champions with his long range Q till they're low enough to kill with your lane mate (if duo lane) or to the point that they have to base, denying them of XP. However it is also a good idea to use your Q to last hit minions if the other team is dominating your lane, around level 2 of Demacian Standard you can Q then E caster minions to get all 3 at once.

Sheen:
The reason we are rushing sheen is with the amount of harrasing you will be doing with your Q the sheen passive should almost always be up and available, that along with your passive is enough to do some nice damage to enemy champions, along with making it much easier to last hit minions.

^ All of the above is the same reason for rushing Trinity Force ^ Along with other obvious benefits it gives you.

Runes are one of the few things I'm not set in stone about. I feel that since I'm Off-Tanking, and armor comes more naturally that it works out well this way, plus a little early game health boost is always a great idea, (feel free to switch them to per level runes)

Again, same reason as above, you still get great DPS without sacrificing much health/defense, and buffing both of the summoner skills you'll be bringing.

By now you should have your trinity force, and whichever tank item you plan on getting, (I put banshee in the guide seeing as AP has been meta lately, and the passive is quite helpful.) I suggest banshee for a AP, CC, or those annoying 1 skill champion (GP's Q) teams to negate much of their damage/CC. For a well rounded team I would suggest a Aegis of the Legion, that is if no one else on your team is building it, as it helps in both AP/AD and it buffs your team (which is always a good thing). And for a AD heavy team I'd pick between either a Sunfire Cape (your ultimate will trap them around you maximizing its damage) or a Thornmail (if their caries rely on AS, aka: Yi, AS Kog'maw, Xin, people like that). Which ever item you chose there should either be close to being done or done, depending on how well you farmed/if you got champ kills.

Team fights are one of the places you can really change the game, if someone on their team makes the mistake of over extending, Ulti that nub and keep him in range of your team this will quickly turn a 5v5 into a 4v5 (and even better if you get their carry) remember to spam your W more for the slow than the shield as it doesn't help out all that much... If you guys have a tank team fights should be a breeze as you're pretty damn close to being a tank (i have trapped 4 people inside my ultimate forcing them all to target me, and got out with 1/2 health and all 4 of them dead (your team can attack them if they're at the edge of your ulti's radius, and obviously ap champs can hit people inside of it as well.

Jungle (red/blue):

It is possible to jungle as jarvan but as I have no life steal, its pointless damage, there will more than likely be other people on your team that deserve red/blue way more than you so it it pointless to take it unless no one else wants and you have nothing better to do, like pushing towers, defending towers, getting dragon, ganking with team, or team fights.

Creeps:

I already stated this above but in case people just jump to this section I will repeat myself:

Around level 2 of Demacian Standard you should be able to Q THEN E (IN THAT ORDER) caster minions for the kill, meaning ever wave you should be getting 3 minion kills, if not more.
The reason you must remember to do it in that order is that if your Q hits your E then you will be dragged to where you dropped your E leaving you behind their minions making you quite a easy target for either harrassment or possibly a kill.

PROS:

Easy Early Game Harrasment
Hard To Kill
Nice Damage with Trinity/Infinity
Nice CC
Distance Closer
Has a Sheild that also slows
^Easy to escape^

CONS:

Distance Closer can sometimes bug and not work
Can be slightly mana intensive if not played correctly
People hate you for being "OP"