Fold the stocking in half long ways. Make a mark 1/2 inch from the middle on either side of the middle. These are the feet.
Starting at the toe stitch up the leg from one mark to the top mark. Stitch from the top mark down the other leg. Cut up the middle between the two stitch lines. (Be careful not to cut the stitches or cut too close to the stitches) You can serge the inside seam but it is not necessary. Trim as needed and turn rightside out. (You can also "shorten" the legs of the tights by sewing across the toes)Once I had made a few pair of these, I moved on to using "trouser socks". They are a little more costly, but they tend to be "thicker" and a little more durable. They also have some neat patterns that look really cute as tights. Just remember to only use socks with no heel.