A friend and I are sewing today-- Saturday is such a nice day to sew!-- and I am "on call" to help out with any glitches. We live states apart so I will be posting some little tutorials on sewing techniques as we go along!
First, here is a way to finish curved facings, such as neck facings and armhole facings for sleeveless dresses, on a conventional sewing machine:
I have to start sewing a little ways further in than the end of my facing, as you see above I put the fabric under the presser foot a bit past the needle. My machine tends to "bunch up" the material if I don't!
I am using one hand here because the other hand is on the camera, but this photo shows that you have to have your hand or hands on the material before and behind the presser foot, in order to feed the curved edge into the sewing area. Keep it nice and flat and manipulate the curve consistantly. I zig-zag over the raw edges -- not over the folded edge, but a ways in.
You can see what I mean in this photo. Clip all those thread tails off of course:)
For a straight or slightly straight facing edge, this is a cleaner finish called a narrow hem:
Fold your edge over about 1/4 inch. Press.
Then fold the edge over again, using that last edge as a guide for folding. .