Xin Zhao is my favorite champion, as I'm always getting fed and owning.
NOTE: This build was built mainly for Xin Zhao, but can also work on any physical melee character e.g. Wukong

First things first,
DO NOT EXPECT TO GO A GOOD GAME
You'll get cocky, then you'll end up feeding someone. Bottom line.
Two,
TRY TO WORK TOGETHER WITH A FRIEND
I always play with my cousin, and the reason we both get fed is because of cooperation and Skype.
Third and last,
IMPROVISE
Sure, my build is good, but what if the enemy Cho'Gath just feasted like hell and is 5K HP? Improvise. Sell that Trinity Force and get yourself an Infinity Edge.

OK, on to the build
This build focuses on DPS, which is Attack Speed and Damage
I know how ridiculous this sounds, but for your rune page, fill it up ALL THE WAY WITH GREATER RUNES OF ALACRITY
The total attack speed increase is 38.1%, which can offset having to buy another item. I also did the math, so don't try this unless you have about 15K IP.
For your Masteries, it doesn't matter EXACTLY which one you get, because they won't help much. Your Summoner Skills should be Ghost and Exhaust, one is for catching up to fast enemies such as Teemo, and then when you catch up you Exhaust them to keep them from running.

Skills
Upgrade the Three Talon Strike first. It's good for early game, because you can stun them for about 2 seconds, which is enough time for your friend to jump in and fuck him up. When you level up, get the Audacious Charge. This dash has pretty good range, and will slow your enemy. The next order of the skills should be
Q, E, W, and R whenever necessary. This is to balance out the skills, because they are all equally good. Before you are level 6, try to be careful. You don't have all your skills and can easily get ganked. After you have your Ultimate however, here is the order in which you attack:

Audacious Strike, Crescent Sweep, Three Talon Strike, Battle Cry.

Before I go on, I need to explain Battle Cry. This skill passively increases your attack speed up to 35%, and when active doubles that increase to 70%, AND each attack you land will reduce all other skills remaining cooldown time by 1 second. If you follow the build, you should easily have at 2.5 attack speed. The effect lasts 5 seconds, so you just reduced your critical by 12.5 seconds. You can keep spamming Battle Cry and get your Ultimate in no time, because it is only 75 to begin with.

Items
Get the dagger when your start, and when you have enough money get the Berserker's Greaves.
Then, get the dagger again, this time for the Black Cleaver
By this time your should be out and ganking a few people
Get Zeal, and go back out there and try to stay alive.
Switch the Zeal for Phantom Dancer
Next is The Bloodthirster, and then Infinity Edge

Here, is where improvisation comes onto play. The last item you get entirely depends on who you are playing with. If the other team has a full AP mage, you'll need Trinity Force. If you know the rest is going to be a breeze, get Phantom Dancers. If the enemy tank is well over 3.5K HP, get Last Whisperer. Try to use your brain, because every situation is different.

Endgame, your attack speed should be maxed and your damage over 300.
Good luck with Xin Zhao, and if I ever come across anyone using my build, I'll gank you and say "Nice Try but it's mine"