The biggest thing you can do as a jungler to reduce damage is from Runes / Masteries.
Specifically, Flat +Armor Seals are usually considered a must for junglers, as the bonus armor vastly reduces the damage dealt to you by the monsters.
For Masteries, the Tough Skin and Bladed Armor masteries (in the defense tree) offer a flat reduction in damage taken, and cause Thorns damage to monsters who attack you. If this extra damage lets you kill them that much faster, that means they have less chances to deal damage.
If you're not using Health Pots liberally while jungling (They work just fine, even while taking damage!), you should start doing that as well.
Finally, the faster you kill monsters, the less chance they have to hit you. Consider Attack Speed Marks for most AD junglers (like Jarvan), to kill them quicker, and take less hits.
So it looks like you're off to a good start, and it'll only get better the more Xp / runes you get.