Shen has been my most-played character since I hit level 30. I have a 62.8 win percentage and average
4.8 kills,
3.4 deaths, and
12.0 assists per game, for a
KDA ratio of 4.9:1. We refer to Shen as "the babysitter" because you can help protect your teammates from their own bad habits (overpushing, bad positioning, etc.). For this reason, he's a great solo queue character. Instead of your teammates feeding kills to the enemy, you can usually end up saving them and getting the kill yourself. Shen is also strong in premade games (where the quality of play is higher than in solo queue) because your lanes can play more aggressively, knowing you have their back.
Shen is strongest early and mid game, but tapers off late game. He is great as a secondary tank, alongside Amumu, Galio, or Rammus...or accompanied by a beefy DPS who often attracts a lot of attention like Mordekaiser, Garen, Pantheon, or Mundo. I prefer to Jungle as Shen, to get to Level 6 as soon as possible. Shen can jungle at pretty high health, so he doesn't really fear being ganked, and he can start pretty much anywhere in the jungle. He isn't extremely fast at clearing the creeps, however, though he's a decent ganker. I think the jungle experts see him as a Tier 1/Tier 2 jungle choice. He is also a strong laner, either solo, or duo. He has a good harass on a short cooldown with his Q (Vorpal Blade), can block damage with his W (Feint), and has some CC for ganks with his E (Shadow Dash). His auto-attack speed is very fast, so he's easy to last hit with. He can handle a 1v2 with ease, but will miss out on creep kills because he lacks an AOE skill to quickly kill a wave.
So, what do you do with Shen? Once you hit level 6, you need to be constantly watching the rest of the map, even if that means you miss out on some last hits. I keep my eye on the minimap at all times, and whenever I see an enemy portrait anywhere near a teammate, I keep my eye on them. There is nothing more frustrating than dying in a 1v1 or 1v2 type situation, when you have a Shen on your team, and he was simply creeping while you died. It is your job to watch the map. It is not their job to ping or ask for an ult. If you don't have the map awareness, develop it! Or don't play Shen.
In a team fight, you want to use your E (Shadow Dash) to taunt as many enemies as you can. You can aim for high priority targets like physical carries, squishy mages, or AOE ulters. Or you can kick off the fight by taunting whoever is close. It is on a pretty long cooldown (8 seconds ish), so use it wisely, and don't miss. It is a skillshot, though it has a forgiving hitbox and pretty long range. Use your W (Feint) to block some damage. It'll shield you from 250 damage at level 5, and has a pretty short cooldown. Use your Q (Vorpal Blade) sparingly in team fights. It costs a good deal of energy. I usually try to just throw it at the squishiest target, or save it for killstealing when the enemy is running away at low health. And of course, figure out the best time to use your ult, usually on your physical carry or mage. You can either hug your carry and protect them, or go after the enemy carry and force them off the field. Both strategies work, depending on your team composition, and that of your enemy.
Late game, Shen should almost never be with the team. He should be pushing lanes and ready to ult to his team if needed. This is why I like Shen as a secondary tank.
Jungle Path
If you choose to jungle, Shen can pretty much take any path. I prefer to start at the mini-golems, then go wraiths, then wolves. After that, either the blue buff and gank top, or the red buff and gank bottom.
Summoners
I use Ghost and either Smite (if jungling), Exhaust, Cleanse (if facing a Galio), or lately, as I realize how strong it is, Clairvoyance.
Runes
I go full tank: Flat Magic Resist Reds and Blues, Flat HP Yellows and Quints. It works out to 145 Health and 22 MR. I have messed around with magic pen and cooldown reduction, but in the end, I prefer the full tank set up.
Masteries
I put 21 into Defense and 8 into Utility (4 into Awareness, for improved exp). The last 1 usually goes into advanced Smite or Exhaust, if I am using one of those summoners.
Skill Order
Generally I start with Q, unless we are going for a 5-man jungle gank, then I'll start with E.
Typically it goes Q, E, W, Q, Q, R. I max Q and E first, unless I am getting harassed like crazy, then I'll put an extra point or two into W.
Items
Start with a
Doran's Shield and 1 health potion.
The three core items in build are:
Once I get 1250 gold, I go back and buy the Merc Treads. I then build the Aegis bit by bit, starting with the Armor and MR parts. Shen's passive gives him increased damage based on his HP, so Spirit Visage is a nice (cheap) item that gives him health, magic resist, and damage. The increased healing from his vorpal blade is a small, mostly-unnoticed benefit. It also gives reduced cooldowns, which is great for Shadow Dash and his ult. This will give him a good base of HP, MR and Armor. After this, I usually slowly build Sunfire Capes, starting with the Giant's Belt, or go for some damage, but really any item is fine. Randuin's Omen is great for the HP, Armor, and cooldown reduction. Zeal is great for increased damage and movement speed. Pretty much any item would be fine at this point, either more tank, or damage, or utility. If I am jungling, I start with a cloth armor, and turn it into a Madred's Razor, before I get my Merc Treads and Aegis, but still proceed the same way after that. You need at least one of those on the team for better control of buffs, the Dragon, and Baron.
Shen is not very item-dependent, so you should buy a *lot* of wards. I try and buy at least 3 every time I go back. I've made it through many wins with nothing more than Merc Treads, Aegis, and one other un-finished item.
I firmly believe that everyone should learn to play Shen because he really helps you develop map awareness, and encourages you to play unselfishly.
I hope you all liked my Shen guide. Feel free to ask some questions. If there is interest, I could probably write a similar sort of thing for some of my other main characters like Miss Fortune, Garen, Vladimir, Xin Zhao, and Tristana.