Important spawn timers:
Jungle Creeps [1:40] / respawn after 50 sec
Ghost Relic (Heal) [1:55] / respawns after 90 seconds
Altars unlocking [3:00] / unlock after 90 seconds
Vilemaw [10:00] / respawns after 5 minutes

Jungling is very different in 3v3 than in 5v5. You get very much farm so that you are even able to play carries in the jungle. Altars not only give gold and AP+AD over time but also give gold when you capture them. They are important and you should prevent that the enemies take it.

Pros:
- High burst
- Mobility advantage due to the map's size
- No wards to detect you
- Jungle sustain thanks to his empowered Battle Roar

Cons:
- Can get countered, risky in blind pick
- needs a lot of practice

For runes I take flat resistance to make ganks and jungling easier, you get defensive items later so you can build MR and armor when you need it. Also I take armor penetration runes, you want as much armor pen as possible with this build.

For masteries I take points in crit stats because of Youmuu's 15% crit chance, Havoc is generally kind of bad. Also I take jungle stats in offense and defense, Rengar needs them.

Begin with Savagery for damage and attack speed, start at Golems because you always start at Golems with Smite, you want to tank them as shortly as possible. Smite the big Golem when it spawns.
You can get the Ghost Relic heal now or after the next camp.
Move to Wolves or Wraiths, you will get level 2 when you finish the big Wolf/Wraith, level up your Battle Roar for tankyness and AoE damage
Move to the last camp.
Move to Golems again and get level 3, smite the big Golem again. Level up your Bola Strike for ranged damage, generally higher jungle damage than with a second level on Savagery and the ability to gank with a slow.
Capture your altar.

Boots

Good for chasing (with ultimate) and getting back to your jungle faster.


Generally a good choice, you can increase your damage output the most efficient way building cooldown reduction.


Good against auto attackers and AD comps, sometimes neccessary.


Generally a good choice against heavy CC, especially in blind pick.

Armor penetration build

Follow this Link to see how my standard build consisting of Youmuu's Ghostblade, Black Cleaver and Last Whisper works. bonetooth necklace also has armor penetration and fits into the build perfectly.
Note that if you activate Youmuu's Ghostblade's active while stealthed it will break your stealth and end your ultimate.

Defensive items

Very good item on assassins due to its passive, generally good against hybrid damage teams.


The best armor and HP combo, it also helps out chasing, Sunfire Aegis can help out jungling though.


OP item. Cooldown reduction, resistance and HP while it also increases your empowered Battle Roar heal.


Anti-CC item that also makes you tanky, don't use it while you ult, it will break your stealth.

Offensive items

Generally good, the attack speed you get from Savagery works well with its passive while you also get sustain thanks to lifesteal, it doesn't give much burst though. The active is good for chasing and extra damage.


Amazing item since the buff, gives everything he needs, burst damage, the Phage passive boost is also good for jungling.


Flat AD, lifesteal and auto attack resets make this item viable, Rengar scales very well with AD.


Good with Youmuu's Ghostblade because of the increased crit chance and damage that helps your burst a lot.


Good defensive item and good for AD.


Good item on Rengar. Your triple-Q combo crits and deals an additional 100% of your AD, so that you scale with 800% of your AD (300% from 3 crits, 200% per empowered Savagery x2 and 100% from 1 normal Savagery). In combination with Infinity Edge your crits deal extra damage making your combo scaling with 950% of your AD while you also get AD from Infinity Edge.

Flash is generally a better gapclosing spell than Ghost in 3v3.
Smite helps you jungling faster and taking 4 instead of 3 camps before capturing the altar at 3:00. Since you're an incredible 1v1 fighter, you're able to counter jungle, Smite helps you with that when your Ferocity is low. Smite is better when you have armor penetration runes, you can do 4 camps and get level 3 with AD runes anyway.
Ghost is kind of awesome if you don't get Mobility Boots already, you can ult and cross half the map in 3 seconds to search for victims. It doesn't break stealth.
Ignite is okay but you're not dependent from it as a jungler
Exhaust is really good and with the mastery you also deal more damage.

Triple-Q Guide for Rengar: Link