This is a nice increase that doesn’t leave a visual impact on your knitting as the Bar Increase is prone to do. You can choose to slant your increase to the left or right, based on the order in which you complete the stitches.
To slant right: Insert your right needle into the stitch below the next stitch on your left needle.
Knit this stitch.
Now insert your right needle into the next stitch on the needle (the one above the stitch you just knit).
Knit this stitch.
To slant left: Knit a stitch. Use your left needle to pick up the stitch that is two stitches below the first stitch on your right needle.
Knit this stitch through the back loop.
Here are the finished increases one row later.