Hi, welcome to my first guide.
I just wanted to tell you that I am a low ELO player, but even so, low ELO players deserve some builds to carry their team.
In this guide I will show what I think it is a good strategy to carry your team as a jungler.

Lets start with the runes.
Core: Seals and Glyphs. You can not get better runes than these, flat armor and magic resist per level, this is a must!

Marks: This is a bit secondary. I put Attack speed to improve the jungle, but 10% isn't much of a good boost. Alternatives would be magic penetration, Healt/mana regen.

Quintessences: A little bit BYOB. Move speed is really good because helps you to respond to ganks, help teammates and jungle faster. You can put 3 of those. Also good is the mana/health regen, allows you to stay longer in jungle, farming and ganking sucessfully. You can also put the attack speed ones, with your marks, you get a nice boots. Flat HP is also good (haven't tested it yet).

2/21/7

The 2 in offensive are clearly for helping you in the jungle, along with the right column of the defense. This is pretty much standard, but I think that 7 in utility are a must. If you prefer, you can put the 9 in utility to get the mastery of buffs, but as you are going to give it to your lane partners, it doesn't really matter, that is why i prefer mana regen, it gets you the blue buff effect, you can spam the W and E as many as you want.

Start with Pendent Regrowth and a potion at lvl1 and go to blue buff. these items should be enough for you to keep jungling until lvl 3 or so. As soons as you got enough money for Philosofer Stone, go back and buy it, if you have money, get a potion too. I usually, when I want to go base, I gank, I risk myself to try to get first blood, and sometimes I die, it is noobish, but in this ELO, it doesn't really matter, you go to base and you get the item, and you shouldn't die more.
Next items are boots of speed and Eleisa Miracle. Reasoning behind this: Boots get you speed and you get to gank a lot easier. Eleisa Miracle get you HUGE ammount of HP/MANA regen, you will be full HP at all timr. really nice item, and also gives you the tenacity so you can skip the mercury boots for another more usefull, since your runes for now will give all the magic resist you need.
Next time you go to base you buy SUNFIRE CAPE, and remember, I said buy it in the next time, you shouldn't die at all until then, you are very very overpowered by now. With sunfire cape you clean jungle pretty fast and in teamfights, having your W, sunfire cape passive, ultimate and E, you should pretty much deal 70% damage just buy yourself to a single target (others may leave with more HP). Risk all you want at this state, you are pretty strong now, even if you die, your team will kill them for sure and you get the money from the assists, which will allow you to buy: sorceress (if they are weak at AD) or ninja tabi if they have hard AD carries.
Next items are standard too: abyssal scpeter gives you the magic resistance/AP you need for the game, with its passive, your teamfights will be very easy.
Buy 2 of the last 3 items, according to what you feel its better. If you need speed, get Shurelyas and Force of Nature. If you need Damage, Rylai and Shurelya.. and so on. Other items can be purchased, at this levvel you are the boss of the game