Think of it as wiping or brushing across the cork. From right to left if you're right handed. More sideways motion than forward.
With exaggerated upper arm movement to mislead your opponent into thinking that you're doing a power shot.
I'm probably doing it wrong...but I use the same principle as how I do a sliced tennis serve.
I'm standing at the back right corner. I do all the same motion (power and speed) of a smash. But instead of hitting the shuttle flat, my racket head is slightly turned (30-45 degrees angle) and I get a sliced cross-court drop. It's successful for me about 60% of the time (ie. still in the court and caught my opponent unaware). Same with the other corner.
^ Heh...and you've caught me out a few times with that shot. What you've described is the regular slice done from the right court, and my description is of a reverse slice done from the left. Reason for the difference is that the action ensures the shuttle stays in.
I like to slice across the feathers but this shot needs practice. What you do is you prepare your stroke as if you would do a clear or smash but just before you would hit the shuttle you turn the racket face and slice across the shuttle so you hit the feathers. This way it is deceptive and I have the impression that it comes down much quicker (maybe through the addiotional spin you give the shuttle). The last part could be my imagination but well :P