(1) Turn under hem 1/4 - 3/8 inch and press. This works well with most fabrics on straight edges. However, if you have stubborn or slippery fabric or are hemming a curved edge, you can stitch 1/4-3/8 inch from the raw edge and press fabric to the inside along the stitching line.
(2) With wrong side facing up, stitch close to folded edge of hem, using inside notch of all-purpose presser foot as a guide (if your presser foot has one -- close to needle not outside edge). I usually end up stitching on top of previous stitching or very close to it. It doesn't matter, you won't see it from outside.
(3) Trim hem very close to stitching. You now have a very narrow hem with a raw edge.
(4) Turn hem one more time and stitch about 1/8 inch from bottom of hem. I usually do this from the right side of the fabric. The weight of the hem will keep it turned to the wrong side if you hold it down a little just outside the presser foot. You can also stitch from the wrong side, being sure to stay an consistene distance from the hem edge. Do not stretch fabric as you stitch.