Why should you play Xin?
In a Nutshell:
Strong core item, fast clearing, strong duelist, pretty tanky.
Description:
Xin Zhao is actually pretty strong because of Titanic Hydra usable effect.
Our champion has fast jungle clear and Tiamat increases speed of clearing multicamps, so you can be everywhere on the map, without losing tempo. He has big damage spike at Titanic Hydra, because it's actually high meta item and gives him AA reset. It allows you to burst 3 AA with knock up at Q, making him a duel monster.
Runes
Lethal tempo increases Xin duel potential, alternatively you can take Conqueror instead, to have bigger sustain in fights.
IMPORTANT: In Legendary tree you take Alacrity or Tenacity. Always look in champ select on enemy team, if they have much CC in teamcomp - take Tenacity, if not - take Alacrity.
Summoner spells
Smite - You are jungler. Obviously u need it to play your role. Dont even think to NOT to take it.
Flash - Its best summoner spell actually. Xin Zhao doesn't need anything else, Flash gives u engage/disengage potential.
Skills
First skill pick order:
E > W > Q
First E because of his AS increase, which gives him good start.
Items
Other pets dont give him as much value as the green one.
Playstyle in a Nutshell
As Xin you should look for early ganks, or safe duels where you can earn early gold lead. Look on objective timers, and try to play together with laners to win fights, to take Drakes and Voidlings/Herald.
At 6th lvl you have huge dive potential with early boost of damage, CC, and long dash, so seek for opportunities.
If you will earn early advantage, try to close game as fast as you can, but always seek for safe trades. If you will be behind, try to focus on earning gold from camps, and single targets with your teammates. In early you will need to play smart, but when u hit Titanic Hydra, you will be much stronger, and you will do much more.