Jarvan is probably one of the best champions to play at lower elos, and carries relatively easily.I would recommend duoing with someone as a reliable damage dealer because you will lack damage against tankier targets later in the game. Though he can be played well in the top lane, he is also very strong in the jungle because of his many forms of cc and gap closers.

i doubled up the galio game to show that these were all played in succesion, and not me choosing my win streaks with jarvan or anything like other n33bs.

In masteries it is better to go with 9-21-0 because you will be mainly a tank in the later stages of the game.
Runes are normal Adc runes becuz noone has the ip to buy armor pen/movement speed runes. If you are one of those people take armor pen quints and marks for better late game scaling.

(Demacian)Standard:(pun intended)wolves>blue>wraiths>wolves>red>wraiths or golems

If the enemy is slow or weak in the early stages(amumu, darius): wolves>smiteless blue>enemy red (use e-q to get through red wall)>whatever you want (killing enemy jungle at wraiths because you have been using those potions right?)

If enemy is fast or will hunt you down in your own jungle(shyvanna, monk, udyr): Wolves>Smiteless blue>red with smite>wraiths>whatever you want

You should start with machete+5 pots because u will die otherwise
First two items you want are madreds and boots of mobility, if you had a successful gank you should be able to pick these up on you first back with 1400 gold. If you dont have a successful gank then get madreds and some wards/pots, normal boots are to weak now. Then get a wriggles whenever you have the gold
Next you should get either warmongs or aegis, warmongs because it is the most OP item in the game and synergizes well with an aegis. Aegis is good for mid games skirmishes/team fights.

Build the bulwark early only if you feel the enemies have a lot of magic damage, otherwise finish it last.

You should finish off with some damage for the late game (tri 4ce, cleaver, maw, last whisper) if your team already has a 2 or more tanky champs (such as having a ryze mid, shen top, alistar bot). Otherwise just build tankier (frozen mallet, GA, thornmail, sunfire cape, randiuns, banshees veil and whatever else you need. I would not recommend frozen heart unless the enemy team has many autoattack scrubs, despite the nice passive and high armor, because of the price and the item not contributing as much as randuins to your tankiness.

You should have at least 4k health and around 150 or more armor/mr with full build, whether with some damage or just tank.