First guide, so sorry if this isn't very good. I am a silver jungler with Xin and I play him a lot. He is my favorite champ since Season 1. I am just trying to teach people how to play with him because so many people seem to do it wrong, at least at lower levels.
One topic that I want to share is that when you are engaging, going ahead and press q before you charge. Sounds simple and it is, but it seems most forget this simple rule.

Below, I have taken my recent history and wanted others to see the scores I am putting up with him. Any help in making this a better guide or comments, I would love to hear/read - even had a penta in my recent history which is always fun and is shown below!

As every one should know, you can't build the same thing every game. If the other team has a malz, vieg or warwick - a lot of times I will rush a sash but not rush to complete it. I think that item is severely underused and especially on a champ like xin that needs to hit things... a lot!

I will skip hourglass occasionally and add in somewhere a BOTRK, trinity force, or defense item. If they have 4 AP champs - I usually go light on the armor and the hourlgass isn't as important. When building the hourglass, make sure you build armguard first and complete it before finishing hourglass to get the added 15 AD/AP.

I know it defies logic to get hourglass initially, it truly does, but it is insane. As you get good with Xin, you will learn to time if perfectly and the extra AP mixes well with your w and e. Like I said above, it you can't make yourself get this item, grab either blade of ruined king or trinity.

Also, remember it is very important to get feral as this lifesteal is critical to your mid/late game and to snowball effectively.

I don't know how everyone puts in the pictures of items and so on but here are some good items on xin that I would consider depending on the game.

Please keep in mind this is from many games with him and for Jungle only. I am not a top player.

Great:
My build items +
Trinity
Blade Ruined King
Wits end if in need or MR
Banshee Veil
Spirit Visage
Sunfire

Good/ok:
Rageblade - if you build Hourglass
Frozen Mallet
Last Whisper
Hextech Gunblade - if built hourglass ( I don't ever build this item)
Hydra
Sash
Spirit of Elder Lizard ( you will fall off late or sell this item)
Bloodthirster
Nashor's Tooth (with hourglass)
The Black Cleaver
Frozen Heart
Thornmail

Bad:
Zeke Herald
Zephyr
Statikk Shiv
Phantom Dancer
Infinity Edge
Spirit of Ancient Golem
Warmogs

This is pretty easy in my thoughts but you will see a lot of different ideas out there, with none of them being really wrong but here are my thoughts for his skill sequence.

Rush E and R

level up q and w together.

My explanation for this has multiple layers but the biggest reason is as you level up E, the CD decreases and it is such a strong gap closer and slow for Xin. With a full E and 2 levels in Q and W, his ganks are so strong!

Again, this is a jungle xin, so I could understand top being different. Also, since I keep a strong lane presence, E just meshes so well for Xin