Hello, my name is Dr Rick Santorum and I am a Diamond 1 player (~2500 elo). I main the jungle, but also have experience in other roles as well. I started playing in season 1, and have been everywhere from 700 elo to the top of the ladder.
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Xin Zhao is one of my favorite champions at the moment. The season 3 jungle is very kind to him, and he has insane ganking and counterjungling potential. While not the absolute best at either of those roles, he does both rather nicely.

Attackspeed scales incredibly well on him and makes full use of the true damage on hunter's machete.
Flat armor yellows are essential on nearly every jungler, due to the large amount of damage reduction they give.
MR/LVL blues are to help you survive teamfights later on in the game, so they aren't very important in the early levels.
Movespeed quints are my personal favorite, as my playstyle is generally aggressive ganking and counterjungling. Attackspeed or flat health quints also work very well with xin.

As you can see in the build at the beginning of the guide, I like to build pure tank xin.

CORE:
Hunter's Machete and 5 health potions are REQUIRED on jungle Xin.
Build the machete into the mandreds the first chance you get. You have high attack speed so you can abuse mandred's passive damage chance.
Boots for xin is a tossup between Ninja Tabi, Merc Treads, and Mobility Boots. You should go ninja tabi if you're still jungling alot or if they have a lot of physical damage. Merc treads are good vs teams with a large amount of magic damage or crowd control. Mobility boots are a high-risk strategy. Only buy these if the enemy lanes are over-extended constantly so you can gank as much as possible.
Locket is borderline overpowered right now. It gives CDR, health regen, armor, and a decent AOE shield. And it's super cheap.
Warmogs is a must. It is the essential item of any tank in the current meta.
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SITUATIONAL:
Randiuns: Good if you are peeling for the ranged AD against melee champions. Even though this item is not cheap at all, it gives great stats and allows you to have even more utility.
Sunfire: Relatively cheap and gives good stats. If you find yourself pushing a lot, sunfire is useful for destroying minion waves along with adding a little extra damage to those around you.
Thornmail: Only buy this if the majority of the enemy's damage is physical. It will SHUT DOWN physical damage.
Frozen Mallet: Useful when you find yourself diving the enemy carries more than protecting your team. NOBODY SHALL ESCAPE
Maw of Malmortius: Strong item against magic heavy teams.
Banshee's veil: Good vs magic heavy teams. None of the MR items are very good as of now.

Challenge
Not the best passive, but increases single target damage by a considerable amount.

Three Talon Strike
This ability is your bread and butter. You can use this to reset your auto attack to hit twice at the same time (by pushing q directly after you auto attack). It does good bonus damage, resets your ability cooldowns by 3 seconds, and knocks people up! Always use your other abilities before you use this one to get the full effect of the cd reduction.


Battle Cry
Your sustain in the jungle and combos are reliant on this ability. Every third attack, you heal for a decent amount passively and activating it increases your attackspeed. Use this as soon as you hit somebody to get the full duration of the attackspeed buff.


Audacious Charge
Gap closer, AOE damage, AOE slow, this ability does it all. The reason we max this first is because of the increase of slow % and cooldown reduction on the ability. Xin is a melee champion, so he relies on this to catch all those pesky runners.


Crescent Sweep
Xin's ultimate ability.
Treat this like a janna ult. A janna ult that does % health damage. You can use it to disengage, to knock enemies over walls, or simply to burst somebody faster. Try to hit as many people as you can, as not only will it do massive damage to them, but you get a defensive bonus for each person you hit. This ability will not knock away a champion you just attacked, but it will knock away anybody defending them! Use this ult and their carry will be left vulnerable and their team hurt and disorientated.

Xin can start anywhere in the jungle and come out ok. There are 3 main strategies when jungling xin;

Traditional route: This path means you go fromwolves-blue-wraiths-red-golems-wolves so you hit level 4 as fast as possible. This path is good if you're against lanes which have good escapes or if you won't get much support from your own lanes.


Early gank: In this route you start wraiths-red. This way you hit level 2 incredibly quickly with red buff. You are then able to gank a lane at the same time the minions get there, but you're level 2 and they are level 1. This is a risky strategy, but if you get first blood it's worth it.


Invade (smiteless blue recommended): A large gamble, but if it pays off it puts their jungler far behind and allows you to take their buffs. You go wolves-blue-their red bush. Don't start red just yet, wait about 15 seconds for their jungler to come and get it. If they come and start to do red, wait until red buff is in smite health and then steal it. If this is successful, jump on them and attempt to kill them before the lanes respond. If you see top or mid leaving lane, GET OUT. Even if you put their jungler behind, if a lane kills you they will get double buff and kill gold/xp, and that lane is basically over from that point on. Very high risk, very high reward.