Just another of my mini-guides/builds. Nothing too in-depth as such and so you won't find a lot of tips/tricks so to speak.

Gold/10 +3.0 (Quints only) Alt: Attack Speed % +10%
Armor Pen +15 (Marks only)
Armor +13 (Seals only) Alt: Attack Speed % +6.9%
Cooldown Reduction +5.24% (Glyphs only) Alt: Magic Resist +12

For the most part these are items that I prefer to build for my jungling Rengar but other than my first 2 purchases, the next 3 come in various sequence depending on how the game is going and who I'm up against.

Mercury's Treads: Pretty obvious choice IMO but you could go with Berserker Greaves as alternate
Bonetooth Necklace: Again, obvious choice, especially if you're ganking early.
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Trinity Force:
Frozen Mallet:
Zeke's Herald:
As a matter of course I always get Phage as my 3rd item along with a Vampiric Scepter 4th. If we are truly dominating early game I rush Trinity Force, if it looks like things are looking bad I get Zeke's Herald and try to focus on bot lane ganks, if things are mostly even I go for a Frozen Mallet and keep ganks in every lane pretty constant. Depending on which items I build after grabbing Phage and Vampiric Scepter I tend to grab Zeke's next if it wasn't the first, Triforce if it was.
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Infinity Edge: This is just one of those filler items that if you actually get to it in a game... then you've so completely won already this is just the nail in the coffin. Some alternatives would be Phantom Dancer, Wit's End, Madred's Bloodrazor, Black Cleaver, & Youmuu's Ghostblade.

There are 3 different ways I jungle Rengar.

Uber strong Leash:
Wolves, Wraiths, Red, Gank Bot, Golems, Wraiths, Gank Mid, Wolves, Blue, Gank Top. B buy first round of items.

Strong/Typical Leash:
Wraiths, Red, Golems, Gank Bot, Wraiths, Wolves, Blue, Gank Mid or Bot. B buy first round of items.

Weak/No Leash:
Red, Wraiths, Gank Mid, Wolves, Blue, Gank Top, Wolves (if backup, Wraiths, Golems Gank Bot. B buy first round of items.

In any situation, Red is going to be your first major camp. Getting a Leash just helps that much more, a very strong leash (one or two teammates to help damage wolves and wraiths and hit Red once to agro for a short time) is an awesome way to start the game. Having someone do the minimum isn't really required but it does make for an easier/safer route to ganking early.