Hello,
this is my first guide ever, I think it is pretty good.
Xin Zhao is an assassin, very OP character, if he gets fed you can pretty much finish the game all bu yourself ( if you fall into a noob enemy team ). Give Xin some attack speed and AD and you can be extremely OP, is he not too hard to play with.

I have chosen Youmuu's Ghost blade( can be replaced by Wit's End ) because I believe it is 10 times better than Phantom Dancer. It gives you extra armor penetration and cooldown reduction and with it's buff , it gives you extra attack speed and movement. Why I have also chosen Mercury's threads is because it gives you extra defense and because you don't need all the attack speed Berserker's threads gives you if you get Youmuu's Ghost blade, but if you feel like you don't need the negative effects shield from it, you can get Berserker's Threads.
For the Builds, you can always choose between Infinity edge/The black cleaver/Trinity Force and Frozen Mallet. It's all about the way you play Xin Xhao. If your team is full DPS, then you probably should go for That will give you some good defense for not much money or else in case of many AP characters in the enemy team, you could also go for that will revive you and it may be very useful in many cases.

After mastery changes, I concentrate on offense tree because IMO Xin does not benefit as much as other champions from defense tree. 21/9/0 setup will allow you to jungle faster and perform even MORE deadly ganks while giving you proper amount of defensive stats.

Credits to Dun1007.