As far as I can figure, this is how the one-wick decrease works. It's a double decrease worked across three stitches - the last stitch on the previous needle, and the first two stitches that begin the next needle. Of course, I'm certainly no expert, so if you know better PLEASE PLEASE PLEASE let me know! (PLEASE and thanks)
1. Extend the last stitch from the previous needle around the index finger of your left hand.
2. Slip the first stitch of the next needle knit-wise.
3. Insert your right needle into the next stitch (the second stitch of this next needle) as if to knit and then pull the far leg of the loop around your index finger through, dropping both the loop around your finger and the original third stitch to create a new stitch.
4. Give the working yarn a tug to take up the slack from that big loop that was around your finger.
5. Pass the slipped stitch over the just worked stitch.
6. The result should be a tidy ridge of slipped stitches along the double-decreased edge. Oh, and maybe have a manicure first if you're doing this for photography!