Slip two stitches, one at a time, as if to knit over to the right needle.
Insert your left needle into the front of them on the right needle.
It will look like you're knitting through the back loop. Then knit them.
You can also do a knit 1, slip 1, pass slipped stitch over decrease on the right and a k2tog on the left. It looks nice when you leave a knit stitch on each edge--do your decreases in the second and third stitches from the edge.