This is a guide to help YOU domminate the jungle with the latest champ, Rengar. However this is a "guide" and I am simply sharing my success with this character and how I did it. So the goal of this, is to see if I pass it on to you so you can dominate the jungle with Rengar...........need I say more?

Personally I built these ruins when I first started Jungling with Warwick. I have not changed them since and I have found them to work on any jungler, so why change?
Armor Penetration Marks and Quintessences
Armor Seals
Attack Dammage Glyphs

For me, I am not a fan of instantly going 21-7 on masteries. Just because a champion spotlight suggests it, doesnt mean it will work for you. From my perspective, if im going to go offensive, IM GOIN ALL OUT!!!!!!!!!! So I take all of the masteries that increase my offensive capabilites, leaving me with 27 in offense, and 3 in defense.

I have done this build several times and every time I have hit a specific spot in my build, it seems like the enemy team has reached the point of no return. I will come back to that later. First off I start off with Boots of Speed and 3 Health Potions. I then follow up with Bone Tooth Necklace, Upgrading my Boots to Ionian Boots, Brutilizer, and Phage. (On a quick side note, the Bone Tooth Necklace is almost always worth it. The only way it isnt is if you dont achieve 9 trophies by the end of the game. The only way this happens is if 1. you go negative 2. you are never in a fight with teamates a.k.a. getting assists or 3. a surrender accured) The next item though, every time I have reached it, the enemy team has reached the point of no return. This is the Vampiric Scepter. For some reason at the point where you are able to slow (Phage), spam abilities (Brutilizer), and gain health back due to the life steal, you cant be stopped. What I mean by this is that if you are a decent player who understands the game, you WILL get at least one kill per team fight the rest of the game. You will do enough damage and it will be fast enough and strong enough that a champ on the other team (unless you went after the tank, in which case, your an idiot) will die with little to no retaliation. From there you simply start upgrading. Brutilizer-Ghostblade, Phage-Trinity Force, Vampiric Scepter-Bloodthirster. At this point I am now sending out a challenge to you. YOU PICK YOUR LAST ITEM!!!!!!!!! At this point you have the other teams attention and they will be looking for you. I personally like kills, but hate dieing, so I go for sustainability in either Warmog's Armor, Guardian Angel, Force Of Nature, or Thornmail, depending on the other teams compisition.

Pros

Hits crazy hard early game
Impossible to escape in jungle
No mana, Just Cooldowns
Enemies fear your passive
7 Skills
He is half man, half lion. how can you lose

Cons

Squishy
Long Lasting CC is your worst nightmare
Have to have good positioning
Oracles will ruin you
Cannot carry

Of course you get your Q first. It's your main damage output so that is an obvious one. From there you can max your E, which is your slow, for "more damage". However the damage increase is so miniscule that it really doesnt help much. I personally max my W, the Armor and Magic Resist boost, second. This provides me with a boost to help me fend off any attempts to fight back by the other team, providing me with more survivability. Now your ult, is one of the coolest in the game. First you stealth, then you can see any enemy champions withen a large radius of you. Then you run up to a target, and pounce on them as if you were in the brush. Almost like a walking bush. BUT WAIT, THERE IS MORE!!!!!! As you are stealthed, your ferocity periodically grows. So in conclusion, you when you press R, enter stealth, sneak up on an enemy, and pounce on them with full ferocity........sounds like a license to kick some *** to me.

Im gonna keep this short and sweet.
Smite-your jungling, DUH
Ghost-can be used to escape, initiat, or move through the jungle faster. so you choose
(optionals)
Flash-best spell in the game, I just dont use it with Rengar

Any other spells you would like to use? No. There isnt. Shut up.

Start off at Red. However while waiting for Red to spawn, I usually hit a wraith with my Q then run to Red before the monsters attack me. This way when Red spawns you already have one stack of Ferocity when your team starts to give you a leash (you dont need one but if you get one, you will have more health, more pots left over, so its just all around better when you get one)then kill Red using your Q whenever possible and Smite. If you do this right you should finish of the Red camp with over 2/3 health, level 2 with a point in your E, and 4 stacks of Ferocity (1 away from the max). You might be thinking "then I to another camp right?" WRONG!!!!! You immediatley gank. You are now half way between mid and bot. Pick the squishiest character and go to there lane. You are looking for first blood here because you want more money right? Of course you do. So go to the bush near the lane you picked and wait for them to go at least half way. If you cannot leap on them with your passive, initiat with your E, to slow them. If you can leap on them, still initiat with your E. If you do this now you are on top of them, they are slowed, and you have full Ferocity. Then the combination of your Ferocity powered Q, a follow up lesser powered Q, Red buff, and any damage your teamate(s) can provide will provide you with the quickest first blood in the game. If you doubt the amount of damage you can do on your own, watch this video. Clearly he uses a different build then I do, but you will still end with the same effect. Happy teamate(s), first blood, and a most likley stunned opponent who now fears your presence.
http://www.youtube.com/watch?v=yZcBlxLfloM
After that just find your way through the Jungle and maintain your levels to be the same or close to your teams levels. Falling behind will give away any advantage you ever had. Get blue if no one on your team needs it, but most likley you can give it to your mid. You dont need it and your teamate will do better in lane, making life easier for you. Get Red as much as possible, this buff makes you do scarry things. Destroy all the camps and make sure to counter-jungle as well (take the other teams jungle). Then make sure to gank whenever you get a good amount of Ferocity (3 or 4 stacks) so that you are always as effective as possible.