The way I play shen is use ap to boost my defensive skills (obviously you use ap) while focusing on my Vorpal Blade so I can do the most damage/healing in the lane for getting the most exp with out having to b.
I up Shadow Dash when i cant up Vorpal Blade because of the tower taunt ability and the team gank-ability. Also if my lane partner is good enough or if you are able to skype/vent with your lane partner then you want Shadow Dash to coordinate the easy level 2 or 3 lane kills.
Feint is just good to get one point in until end game because you need all your skills on any character you play pretty much.
Also since you will get AP items fairly early your Feint will also be better then you would think it would be with only one point in it.

So my strat is that I start with the ruby crystal because you will have SD by level 2 and can use that for your movement speed. I go top lane so im closer to the golem buff for later on. With that health boost you can harass pretty well beacuse most champs will take 2 to 3 attacks to damage the health from the ruby crystal giving you an edge to do your damage to them and tank for your partner. If you get harassed too much play at the tower, Q the strongest/highest hp mob and attack it so you gain health. Slowly but surely you will be back to full in no time. Next if you can help it, b when you have enough gold to finish Aegis (preferably when you can get boots of speed 1 also). If you cant finish Aegis because you had to b early or because you died then grab the boots first. With your partner coordinate as best as you both can to demoralize the people you are laning against. When you hit level 6 and get your ult, show them that you can destroy their faces by telling your partner to tower dive when they have low enough hp to tower dive them and get the kill. You ult to your partner giving you both the shield from your ult on top of you have your W to tank a hit from the tower. By level 6 you should also have your boots completed (ninja tabi if you need armor over magic resist) and at least the Giants Belt so you can comfortably dive.

After you dive and get the kill you should either push or b depending on if your mobs are letting you push or if you need to b because you have low hp or if there are MIAs.
Really just be smart after diving thats the simple way to put it. Alot of people get too cocky and think they can stay longer then they should. B-ing a second late is the difference between living and dying sometimes.

Grab Golem buff next (unless you have a jungler) and make sure your tower is defended if it needs to be. If you need to go tower first do that, then get golem. On shen golem is a must have because of the CD reducing that it gives you can ult sooner, VB more, and there for rack up tons of assists and some last hits with VB. Since your a tank try and get as many assists as you can since you are trying to carry with assists. If you get too many of the kills via last hitting every time your DPS characters will not have enough damage end game.

So from here you should definatly be ganking the obvious gank choices. Try and get your lane partner to follow you around the enitire game so you have some serious damage following you and you will not die very often doing this: you initiate [you have aggro] then you lose aggro to your partner and you SD to them to get it back and then your guys win the fight! That should be happening while your enemies are in the foolish, non 5v5 stage of the game. Id say between level 8 and 12. You want to have your lane partner (if he is following you good) be a bait when your ult is up so you can ult to him to either let him escape if its a fight you cant handle OR suprise the enemy and SD to him, VB him, Ignite him, VB again, SD again and dead. really easy.

by level 13 or 14 you should have up to Sunfire Cape in my item build. You will rack up assists with SFC along with its a good source of hp and armor.

End game in 5v5 fights you want to initiate your teams fights by being fearless. Dont run up then away then back up and then away trying to think if you should rush in... Just rush in and start the havok! when you run in your team should be pumped and like "lets do this look at our tank go!" and they will just dominate. Make sure YOU mark targets to focus, once they are dead, mark the next. Obviously you mark the DPS champions first.

Remember, this is if you are all there. If its a 4v5 dont rush in, just defend your tower.
If your team is downie and doesnt help you when you tank, you can try and escape with your E and W and flash. If they arent downie and you guys get 2 easy kills (which you should at least get 2 kills each team fight) then the rest of you should push then while its a 5v3 or 4v3 (sometimes one guy dies, but this isnt a guide for them so im not going in to details on how they should play). if they are at tower with half hp and you have half hp, show your team that your boss and dive them. they will follow since you will have tower aggro.

pretty much once you have all your items at 18 your unstoppable because you should have force fed your lane partner.
When me and my homie play he plays Tristana and I go 10/5/30 and he goes 20/3/15.

Hope this guide was helpful. its my first guide. This is for competent players.

If you want to do the most damage you can as early as possable follow my skill sequence.
If you want to build tanky then i would get the following:

1: Vorpal Blade
2: Shadow Dash
3: Feint
4: Shadow Dash
5: Feint
6: Stand United
7: Vorpal Blade
8: Feint
9: Vorpal Blade
10: Shadow Dash
11: Stand United
12: Shadow Dash
13: Shadow Dash
14: Feint
15: Vorpal Blade
16: Stand United
17: Feint
18: Vorpal Blade

no need to bother with anything expensive. be good and you wont need anything other then straight up Ap at 18 blue runes, Magic Pen red runes, HP at 18 yellow Runes, and Ap at 18 Quints. You want "at 18" runes because you are going to be a better end game tank.

you definatly want 15% magic pen to stack with your runes and your VB will do more damage (it gets to where its hitting super hard) you also want the Ignite talent so you get 10 free Ap which is good for early ganking.
You dont need tenacity. 4% dmg reduce isnt bad, but im not building him like a pure tank, he needs a little punch to him and thats why id put the point in Ignite instead of tenacity.
Depending how you want to play, switch those.

first is Ruby Crystal for HP advantage early.
Then you get Aegis if you have enough money if not buy boots and magic mantle or cloth armor depending on who you are laning against.
Then you finish Mercury Treads (or ninja tabi if they have no AP champs with little stun).
Build the Ryjals Scepter starting with Giants Belt (if you cant finish it) next.
Get a Sunfire Cape starting with Giants Belt again if you cant finish SFC.
You should get Thornmail if they are physical damage, or a Banshees if they are AP
Then get a Zhonya's Hourglass for the nice AP boost along with the use effect it has.

Get Items that you need to counter your opponents. DO NOT just build what i suggest. If they have no AD champs then build strictly magic resist substituting Sunfire for Lich Bane and subbing Thornmail for Banshees.