Check out this article.
I personally use the "bat wings." My gym does not have kettle's so i just use dumbbells. I lay on the bench face down, and pull the weight into my arm pits for a slight pause contraction. It is limited movement, because the weight hits the floor on the way down, but that makes it challenging because you never get a full rest between reps. The article does a good job of explaining the movement.
This article (and the first article in this series) does a great job of talking about the shrug. It is very long, and very thorough. I would recommend looking at the second link and looking at the overhead shrug. The overhead shrug is a different movement in that you are almost using your scapula's to press weight up, similar to a military press.
The movement in this exercise really stretches out your back, giving your scapula's the ability to retract and settle into your new posture with strength. I trick to doing this different than in the picture is to do them in the smith machine, so you focus your movement very strictly, as opposed to supporting free weights which can shift weight into your delts/tris/lower back very quickly, and defeat the movement.
Also stretch stretch stretch your lats. 30 sec.'s to a minute between working sets. This will work your posture back into the retracted position you are looking for, and you will also feel better in general.