“Let your plans be dark and impenetrable as night, and when you
move, fall like a thunderbolt.” -Sun Tzu

That cannot be more true for this Xin Zhao build. We will focus on attack speed (Xin Zhao benefits from this more than anyone)to mold him into a very aggressive ganking machine.
With an assortment of attack speed, lifesteal, and critical chance items as well as an offensive mastery and summoner spells to match, Xin Zhao can become the most dangerous and unpredictable champion on the battlefield.

This build must be played with extreme caution. A lack of armor and magic resistance can be your undoing if you do not read the battlefield well and/or support your teammates. Xin is an effective opportunist that can take out opposing players in seconds before their teammates can react. You should always be on the move and keep the enemy guessing where you're going to strike next.

This build is very gold-dependent in the early game.
The order that you attain these items will vary depending on how the team rosters look. If the other team has a lot of ranged/tanks, consider getting lifesteal a little earlier to improve your battlefield endurance. Extra health potions can help you take more heat early on. If your gear is lacking mid game, some quick jungling or solo laning will help you catch up (but don't dive too deep, because you're an easy target!). Your superior attack speed and damage will make your lack of armor and health very deceptive, so baiting can work very well.

Skill hierarchy is as follows:

> > >

Challenge Xin's passive ability allows you to heal yourself with every third swing, so high attack speed improves it's effectiveness. You should always try to be attacking something to take full advantage of this skill.

Three Talon Strike is an excellent skill for disabling an enemy as well as doing quick damage, especially if used with Battle Cry. It's also great for early lane harassment if the enemy is easily reached.

Audacious Charge is used simply for utility, so only one rank is sufficient to start with. Pick up one rank at level 4 for harassment purposes. It also has a slowing effect, making it perfect for running down a lone enemy.

Battle Cry makes Xin's attack speed directly related to cooldown reduction. The more attack speed you have, the more you can use your skills against an enemy or to dispose of minions quickly (and the more health you restore to yourself). This fact also makes the enemy very unsure of Xin's cooldowns and therefore wary of 1-on-1's with him. You should use Battle Cry every chance you get.

Crescent Sweep is a great AOE damage dealer. 20% of an enemy's health (plus a bonus) can turn the tide of a fight VERY quickly (works great on tanks). If a team fight occurs, try to blindside the enemy with crescent sweep, then pick off the weakest link. Sweep is also an essential ganking tool.

Greater Mark of Desolation Greater Seal of Attack Speed Greater Glyph of Attack Speed
Additional attack speed as stated above is great all around for Xin Zhao. The extra armor penetration will help your fast strikes deal more damage. As mentioned, this build is a full-blown assassin. Flank, gank, and RUN.

Greater Quintessence of Desolation
Once again, more armor penetration = more damage = faster kills.

Exhaust is great for de-clawing enemies momentarily in battle. Turn the tables on an enemy by making them waste their cooldowns on you while exhausted, then move in for the kill. It's also very useful as an escape tool as Xin Zhao does not have an effective escape method. If you find yourself in too deep or about to be ganked, exhaust the strongest enemy you see and make a break for it. It is used well alongside Flash or Ghost, which are great for the same purpose.

Teleport is a decent alternative too. It's good for getting right back into the action, especially if you're picked off early. You can save precious time by teleporting back to battles, or use it to cut off enemies in a far away lane. This again adds to the enemy's uncertainty about Xin Zhao's whereabouts.

As mentioned before, this build reinforces Xin Zhao's strengths: the ability to deliver devastating damage and cover lots of ground. Laning with a ranged or tank teammate is reccommended, as Xin Zhao can get picked on easily from a distance in the early game. When fighting champions, head-on attacks are discouraged (unless you're harassing in a lane), so find a good spot to ambush the enemy. Avoid taking on tanks alone, at least until you have enough attack damage/lifesteal to hack through their massive health-bars. Baiting with a teammate near a midpoint is an excellent way to snag multi-kills: let them get very close to your hiding spot, charge in for a quick slaughter, take out any stragglers, and get out of sight just as quickly. CC from a teammate amplifies your effectiveness many times over. Once you gain a reputation as the ganker among the other team, you can expect them to come after you in groups- so stay relatively close to teammates.
This strategy overall is high-risk, but higher reward if done right.
I tried to make this as short and sweet as possible- after all, the best research you can do for any character is to practice yourself!

Thanks, and PLEASE VOTE!