I've been jungling a lot recently, especially as Jarvan. On my first clear of the jungle I get really low health, often times preventing me from ganking. Is there anything I can do to prevent this? I'm level 23, so I don't have all runes/masteries.
Edit: I appreciate the feedback, but there's no reason to recommend masteries/runes that I've already taken. I linked my runes and masteries for a reason.
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.
When jungling, you want to take the right-most masteries Tough Skin and (optionally) Bladed Armor. They might not sound like much but 2 damage off each hit compounds and the thorns effect shortens jungling, meaning you take fewer hits and less damage.
Considering you're L23, you qualify T3 runes which means you should be buying flat armor runes to reduce damage further. In fact, make most of your rune purchases the flat version. Early game is extremely important for every jungler and every little bit helps.
In the defense tree masteries, use the Tough Skin and Bladed Armor to increase damage applied thus shortening the time you take damage.
In the offense tree, Butcher will shorten jungle time more than 1% attack speed (+2 damage > 0.00658 extra AS). Extra points should go into Butcher before Fury.
Saying that (based on probuilds.net and other guides), J4 is a attack damage jungler, not an attack speed one. So AD runes will take you further than AS runes.
Are you maxing E on J4 to increase your atk speed for camp clear? Beyond that, J4's passive benefits from frequent target rotation rather than attacking a monster one-by-one -- be SURE you're taking full bonus from his passive by switching to a new target every time it's up. This increases your total DPS = less time spent taking dmg = faster clears = more HP.
The current accepted answer recommends A/S on J4 -- I strongly disagree. He's one of the few that benefits from ARpen marks because he already has A/S, AND he has Arpen from his Q and passive so you can do near-true damage with Arpen + Q + early game ganks.
