It's my 1st build so give me a break.
Now, Xin Zhao can carry allot but you may have some problems.
The tips I give you is here in this build.
I can resume the tips by a few words:
Farm,Gank,do lizard and help your teammates aswell.
Please rate.

HP-Health Points
MP-Mana Points
KS-Kill Steal
MP5-Mana Per 5 seconds
HP5-Health Per 5 seconds
AD-Attack Damage
AP-Ability Power
AS-Attack Speed/Attack Rate
LS-Life Steal
CS-Critical Strike/Critical Chance
CD-Critical Damage
MIA-Missing in Action
OOM-Out of Mana

Pros
Great Ganker
Can be the highest DPS in the game
Not squichy
Good CC ( Knock Up and Slow)�´
Good farmer
Great pusher
Bruiser
Cons
You will be focused in team battles
Depends on your kill/death ratio , if you don't have a good or normal score you will be useless

Runes:
I put 18 seals because if you think Xin Zhao needs some mana regen you could buy the seals , just choose 9 of them.(Choose 9 mana regen or choose crit chance but you can also mix a bit)
You cannot discard the armor pen. and the cooldown runes aswell.

The boots can be replaced by Mercury's Treadsdepending on the enemy team.
If you are having trouble in catching your apponents then grab Boots of Swiftness.If your game is going good then buy a Sword of Occult.

Good Choices:

Exhaust
-Good for slowing and now it was buffed.
Ignite
-Great certain killer , if your enemy tries to run away ignite him before and you will have chance for a kill.
Flash
-Good for engaging and getting near the opponent.
Cleanse
-Great life saver
Ghost
-It will be usefull having ghost so you can gain up your opponents or engaging a teamfight or even ganking , etc.
Bad Choices:

Smite
-Your not jungle...
Clairvoyance
-Simply useless
Rally
-Simply useless
Clarity
-With your runes you won't oom(out of mana)
Revive
-Simply useless

Farm allot and most important grab a Lizard buff so you can have more chances on killing your opponents.
I put in masteries the Utility Master so your Lizard buff will last longer.

Gank allot.
Call MIA's.
If there is any opponent jungling then buy Sight wards.If there is a stealth character like Twitch and Evelynn and she/he is making trouble ganking your teammates or even you , buy a Vision wardor an Oracle