From what I have read on Deft Strike, I think it works for when you attack when hidden.
Typically if you use an action to leave your hidden space, you lose the hiddent status at the end of your action. For most characters leaving a space that allowed them to hide will then make them visible at the end of this movement and typically requires a move action, then any subsequent attack requires another action (standard action) to attack, but now without the benefit of Combat Advantage.
As Deft Strike allows move 2 squares AND attack with a standard action, you don't lose the hidden status or Combat Advantage until after the standard action is completed.
After using Deft Strike, you can then use your move action to regain superior cover or total concealment and make a fresh Stealth check to become hidden again.
The easiest way to achieve this is using the corner of a wall.
