With this guide, you should still play a little safe. So its important to know when to engage in a teamfight, myself I like to stay in the back until the most enemies have lost some hp, then knock them up in the air with my E Q combo for so landing an ultimate, making my team able to come in and fight again.

Its not always you can save your allies, if you know you can't, stay back. If the person gets mad at you, you tell them your tought when you walked away and do good teamwork with them from then.

You could choose to have more offense masteries, but with this build and those runes, I really don't recommend that. Stay defensive you know, being a crazy Jarvan IV kills you fast.

Of course you should also consider some Armor and Magic Resist runes too, because you may become the first targeted.

Teamwork is as important as always, always stay close to your team and help them out in a team fight. But as I said, stay back for a while and make them think that you are not there. Then strike with knock-up and ultimate.

Pros
-Nice Damage
-Good in team fights
-Almost never dies
-Takes care
-Hard to kill
-Wins most lanes

Cons
-Easy to kill
-Destroy team fights
-Runs away even with the chance to save an ally
-Only farms
-Easily ganked
IF YOU ARE PLAYING JARVAN IV, MAKE SURE YOU'RE GOOD

Farming is important, but make sure that you are safe. Also never forget about your team, ward up in the closest bush and watch your team at any time. Also the ward.