I had a black pencil skirt in my closet, so I used that as my pattern. I laid the store bought pencil skirt on top of the fabric.
I traced the outline of the black pencil skirt and added 5/8" seam allowance. I also added 1 inch at the top for the casing for the elastic.
I cut out the skirt and that's it. I made the pencil skirt entirely on the serger, minus the casing for the elastic and the hem, I used the sewing machine for that. I serged the side seams where the serger blade was just skimming the fabric. Fast, simple and easy.
MY PREFERENCE is to have a seam on both sides of my pencil skirt. I know there are some that have the seam in the back, I get a better fit when there are seams on both sides.