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:
- infinite gapclosers in the jungle
- by far the best early game of any champion
- stealth
- burst
- sustain

Cons:
- fkin nothing
- hates hard cc
- passive bugs pretty often

Max Q first and take it on level 1 for crazy damage. Max W secondly for tankyness and AoE damage.

Ghost is frickin insane on jungle Rengar, he just walks in lane and jumps around, gg FB. It also helps with his ult and for backdooring.
Flash is standard and can be used to close gaps to bushes to have double gap closers.

I rush Triforce in every match, basically Phage first, then Sheen or Zeal, doesn't matter.
Last Whisper is amazing for its price at the moment and works well in combination with Brutalizer, Last Whisper and Brutalizer works the same way Void Staff and Sorc. Shoes work in combination, it's just that building AP on mages is more efficient. You will also not have any problems with armor so you can build Blade as your 3rd item if required to counter HP stackers and destroy tanks.
For defensive items I go for the currently most gold efficient items listed above, CDR is damn good on Rengar while tenacity can be neccessary if not purchased through boots.