Jungle is probable one of the best champions in terms of utility, pressuring lanes, dueling, and team fights. He can be built tanky to take the bulk of damage, or as an assassin/aoe fighter fopr maximum damage. Xin Zhao is most effective at his assassin and fighter capabilities. This guide will be oriented around utility and assassination as Xin is best played this way (for fun and competitive purposes).

I prefer this rune page for non-ranked play due to its sustain. The life steal combined with Xin's [battle cry] passive is very good early game and help Xin stay in the jungle longer, pre any lifesteal items.
The armor helps when ganking top and bottom laners.
Attack speed also syncs with his [battle cry] as well and helps him clear the jungle faster.

Starting The reality blue buff will not last forever so taking 4 biscuits and 1 mana potion is ideal. Taking one biscuit mid-buff clear will keep Xin at full hp and allow him to gank at level 3 (huge if enemy bot lane is pushed and can be killed).
DPS Build Post 3
If lanes are pushed consider buying wards for them. As a jungler, vision is benefical not only for you but for others as well. It can allow your team to spot ganks and allow you to counter gank. it can also allow you to invade safely for the 2nd and 3rd red buff of the game. When reasonable back and pick up at least a Spirit stone and Boots. If funds are enough, go straight for the elder lizard so you can farm faster.
Post 6
If you are Killing or Assisting more than you are dying go for the ravenous hydra so you can clear faster, apply map pressure, and sustain much more.
If KDA is negative, go for the black cleaver for needed hp and more damage in lane. Also go for a guardian angle to counter ad and ap.
Post 9
From here decisions must be made. If the game is going good go full out AD, pressure lanes, assassinate carries and allow your team to take objectives. If the game is going bad, your last three items should be tanky. Guardian angel and spirit visage and banshees veil are all viable options vs ap. Ad can be countered with Randuins , Frozen Mallet and guardian angel.
Here on out Xin falls off if he is not ahead. People start building up damage or armor and begin focusing him due to his squishiness( if he is behind) or his damage. Take objectives as fast as possible and look for opportunities for easy kills.

Team Fights:
Xin's early team fight is amazing at level 3, especially if he can reach it before anyone else. From here Xin has a gap closer and a knock up.
Mid game: Xin remains an effective assassin and can duel most champions and isolate a champion with his ultimate.
Late game:
Xin becomes either an off-tank or an ad carry and can continue to isolate targets and even kill but cannot be relied on as a main tank.