Welcome to my first build . After playing Xin for a lot of games I'm posting this build hope it helps.
Before we proceed some points to be noticed are :
1. This guide is meant for players who like to go in , and kill . This ain't any health stacking build where u will last long to survive a long a team fight or troll around in map. Its meant for aggressive players who like to jump anywhere on any1 , kill it and get out.

2.This build is based on Xin passive (Tireless Warrior) , where he gains health by striking anything he can be strikes.

All Runes mentioned here , do one thing that to increase your attack speed . It may have teo effect depending upon play style.

PROS:
1.No need to waste 2500+Golds on Phantom Dancer or Madred's Bloodrazer.
2.You will be doing damage faster than other player in lane , this helps you to regenrate ur health faster with passive and life steal.

CONS:
1.A single disable or exhaust can change ur momentum as Xin will always need to strike something to live longer.

1. Start with Vampiric Scepter
2.Get Boots , u can choose your own boots depending upon opponent play style .
3.Build a Wriggle Lantern , its good for early 1vs1 as it provide plenty lifesteal and armor , its passive is great too , but dont rely on it as 3 minute cooldown for ur own ward is really long.
4.Get Black Cleaver , I've seen many players especially tank putting armor in and then harrasing team mates . Black cleaver passive cleary make them run as when they realize their armor has been compromised there is nothing on them to survive.
4.Get Blood Thirster , by this time every1 should be running away from you as soon as you appear. Now blood thirster comes in to play , u gain more damage and lifeseal everytime u kill a minion.
5.Get 2 Infinity Edge , yes its a costly part but take ur own time with patience and slaying enemies you will get them , if some1 on opponent team has got some real heavy ad sell ur Wriglle and get IE ASAP.
6.Finally get another Black Cleaver to increase ur attack speed get damage and confront those tanks who have grown.
7.If games last real long then put elixirs on ur champ , if there is some invisible unit in opponent team get oracle too.

1.Stay from jumping right in middle of team figts , Xin is too much vulnerable so stay a lil away or in end of ur team mates who got some CC effects later u can jump when some1 is stunned or slowed or suppressed.
2.Save your team mates from suppressing ultimate , of like that if Warwick or Malzahar . using ur Three Talon strike quickly will end their ulti.
3.For Nunu and Amumu ultimate just stay away and watch , u r no good dead better watch . As soon as they start their ulti just bump them using ur "Q" htis will provide and exceptional opportunity to ur team mates as opponents will be disoriented and have no CC support.
4.Never run away from fast moving champs , like Teemo or Ashe or a chasing Trynda . These champs rely on their abilti to catch u , slow u , or kill u if try running . Best is to Charge them with "E"(Audacious Charge) and then quicly kill them or die while lowering them to very low HP and watch ur team mates finish them .
5.Dont waste ur ulti. Wait for right moment and keep eye on ur enemy health bar , cause later in game they will regenerate health faster then ur ulti damage .

Farming is really important for this build , dont leave ur lane until forced too do so or u get their turrets.
Look for low health minions and quickly kill them . If your abilities are on cool down , wait for some time and engage WarCry("W") it will help u clear minions faster and also will reduce cooldown of ur abilities by 1 second per hit.

1.Against Katarina
She loves her ulti and will pull it whenever she like it , best is to stay away and let tanks take damage . If u see kata roaming in wilds just attack her , once u start she will run , use exhaust and kill her

2.Against Jax
Jax depends a lot on AP+AD , if he appears best is to look for some CC effect on him cause he can easily stun u .

3.Against Swain
No need to engage Swain if even if he's on low health and u r too , he will engage his ulti and quickly cripple u.

4.Against LeBlanc
She does a tons of damage with her combo , and her passive is really cool , just w8 for right time and use ur ulti to kill her and her clone at same time.

5.Against healers (except Alistair)
Focus healer first , in an order of (Soraka->Sona->Taric->Nidalee->Alisatir). Healer can destroy ur confidence by healing unit quickly , best is to push them and harras them .