I will keep this guide as short as possible because I hate a long guide myself.
If you think I forgot something or have feedback I'm open for that and let me know.

Why this guide?
Having my fair share or bad placement games and ending up in Bronze 1, one thing really caught my attention. The lack of good junglers (and ofcourse the leavers flamers and negative attitude). I thought HELL NO! screw you Riot and your faulty system. (4 out of 6 placement games I lost because of leavers/rage quit).
So I decided to master a champion, I started out with Malzahar midlane, which I won most of the time, yet my teammates lost most of the time and our jungler stayed in jungle to long or just failed at ganking. Then one game I played against a Xin Zhao and he opened my eyes and I fell in love with him. I went training and discovering this champion and eventually mastered him.

Even though I like other roles as well, most people really don't know how to jungle and find the balance between being in jungle farming while keeping an eye out for potential ganks. This frustrates me because even when I was having a good game as midlaner we would still lose the game because of the jungler who doesn't know how to jungle and failed to support the other lanes who needed ganks/help.

Jungling isn't easy, you need to ward well, Always pay attention to the minimap, always ping when you see danger, farm in jungle, and spot good moments to gank and the hardest part is to find that balance. Even I find it difficult and still make mistakes. Those mistakes most of the time end up having me killed. Which are good learning moments.

I always start Krugs, because Xin is a attack speed champion the stun buff is superior to the buff from Gromp.
After that it's Red buff where I use my first potion. After red you have a few options.

1 You can look if it is possible to gank bot or mid lane.
2 You can invade enemy jungler (most of the times there red buff) and wait in bush untill they almost got the monster down and then kill them. Only do this when against a jungler that has a weak early game jungle like Kayle.
3 you go to blue buff.

Most of the times I do 3 though if you see the chance to succesfully gank a lane or the enemy jungler ALWAYS do it!

After blue I look if i can gank top lane or pressure at least, if not I kill river crab and continue my jungle route to Wolves (without smite) then Gromp (without or with smite) and then Raptors (with or without smite), then I look again for a possible (succesfull) gank if not I go my first back. After this it's just getting your Devourer into a Sated Devourer and ganking as much as possible, while clearing the jungle, keep warding and paying attention to dragons.

The most important thing is to pay attention to the minimap and what is happening. Watch out for your teammates and ping if there is danger or someone is missing. You may think they can do that for themselves and yes you are right. But people can be focussed to much on other things that they miss the danger.
So if you want to win just get over yourself and do it, these things make sure you win games.

These items combined together with Xin Zhao Make you nearly impossible to kill, you have a lot of sustain and still put out a lot of damage. People most of the time make the mistake of building there jungler to squishy to much focussed on damage. So they die to quickly. This way you can engage, (tank) survive and kill people pretty easy. Believe me BotRK combined with Sated Devourer and you masteries and runes give you enough damage that the enemy will run away from you.

Most of the time I pick black cleaver in a balanced team, It gives HP, more CDR which is always welcome and Armor Pen which works extremely well with your attack speed.

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When you need to be more tanky because of a auto attack champion like tryndamere or a (fed) adc, buy Thornmail

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If they have a lot or magic damage consider buying locket.

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If they have a lot or magic damage with burst and possible cc (like Annie with her ult + stun to name one) then consider buying Banshee's Veil otherwise I still think Locket is the better item here.

Ghostblade Is a good item, which you can buy INSTEAD of BotRK. Ghostblade makes ganking easier and you have more armor pen, but it does not work as well your core as BotRK so I would say no only if you are behind and have trouble ganking.

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Trinity Force is nice it gives all round stats but it's expensive and looking at the core I rather have Black cleaver, Though in some situation Trinity Force can work wonders.

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Sunfire cape is a viable last item, it gives HP armor and a aoe dmg aura. But the passive's from the other items are more usefull in teamfights especially late game.

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Warmogs's can be good when you are dealing with true damage, though if they have 1 or more BotRK I would not get this and go for a Sunfire cap instead which also gives you some armor and HP. If they got a vayne, this may still be a viable item even if she builds BotRK.

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If they have a few fed AS based champions pick Frozen heart for it's armor mana CDR and slow aura. But most of the times Thornmail is the better pick here and I will explain why: 1. You already have Randuin's Omen, which gives you also apply's a slow on your attackers (it's not an aura I know). (Randuin's Omen is better then frozen heart, because of it's HP and active imho). 2.Frozen heart is also a beloved item with the supports and having 2 of them is not needed as they do not stack. 3. Champions with high AS mostly do that damage as basic attacks which in this case means that with you sustainability and you hp etc, these champions are killing themselves on you with thornmail and that extra AS slow from it's aura will not give you that. Invisible text! Update With the recent update I would not get this item anymore, Randuin's Omen with it's Crit reduction, and thornmail with it's armor scaling are more superior to Xin and to his core.

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I would not get this item, only if I was fighting an AP heavy team. If you follow my core, you are already nearly indestructible and if you do however find yourself in a fight where you die (which mostly happens if you fight 1 vs 3 or more) then this item doesn't really help either, you will die the second time as well. Maybe your team can rush to you and help or you can kill one of the enemies before they kill you again. Yet this item still doesn't help you much and other items tend to be more useful. And for the record you should not be alone without vision of enemy team and fight 3+ vs you alone, unless you are really fed. (you probably wouldn't have bought this item then.