(This process works with a serger. If you do not have one, it is best to turn under the raw edge of the hem toward the fold and enclosing it before stitching with a twin needle.)
Sew a line of stitching along the bottom of the skirt 1/8 inch less than the distance you wish to make the hem. Press to inside along this line of stitching so that it does not show from the right side (stitching line will be approximately 1/8 inch above fold).
Set up your machine to use a twin needle and thread both needles with matching thread. Begin stitching on the outside at a seam and sew around skirt so that you are sewing on top of the serged seam (Hold hem so that you can feel the ridge of the serged seam underneath your twin needle stitching. It is best to sew the double seam just below the edge of the serged seam or down the middle of it so that your zigzag on the underside of your twin stitching is on top of it, giving you a firm base to prevent tunneling.
Press seam from right side.
I would usually allow the garment to hang at least overnight for most fabrics before beginning the hemming process.
This technique can also be used for narrow hems with one row of stitching instead of a twin needle. For a 1/4-inch hem, I stitch 3/8 from the raw edge, and then serge the edge with a 3-thread narrow O/L (You can use 4-thrad but it will be wider). Turn up along the line of stitching so that it does not show. Stitch from the wrong side down the middle of the serging or close to the left edge (near where raw edge was). The stitching is lost in the serging on the wrong side and forms a 1/4 hem on the outside. Be careful not to pull the fabric as you stitch or it will form wrinkles on the outside on the bias sections. You can sew from the right side by feeling for the ridge of the hem edge and stitching just to the right of it, but I find that if I go slowly from the wrong side, my hem is perfectly in line with the bottom of the skirt.