I used the last week to intensely play Shen. I really like to play a tank which can contribute so much to the team (his Taunt and Ult are just awesome).
I usually play him on Top lane where I face mostly Bruisers and Tanks.
So when I play against them I sustain my lane, try to harass with my Q (Vorpal Blade) and farm. When they overextend, I try to punish it, but altogether I think Shen is not offensive enough to gank alone. So I prefer to gank my enemy when the jungler shows up.
This works very well against melee champs like Xin Zhao, Shen or Nautilus.
Now when I play against a ranged carry on top I really tend to fail. For example, I can't do anything versus a Teemo. All I can do is try to safely farm with my Q. If I try anything else, he goes for me, and I am not quite sure what I can do about it. I can't bring do burst damage to him since Shen has no burst.
For example when I play Riven (my main char) versus Teemo (or another ranged carry) I wait for them to overextend a bit and then go in, do some real damage and go out. But with Shen this is just not possible.
So any advice?