First, baste stitch the seam on which the zipper will go.
I basted right over the facing to help hold it down.
This is the seam on which I will place my zipper.
The zipper is place face down directly on top of your basted seam. Pin in place.
The plan is to sew along the right side of the zipper teeth first, pivot the fabric at the bottom of the zipper to sew it closed along the bottom, and then pivot the fabric again so I can come up the other side back to the top.
You must use a zipper foot so the foot and the needle don't hit the teeth, thereby breaking your needle.
Next, change the stitch length back to your normal setting, and be sure to lock stitch the beginning and the end this time.
Here I have lifted the presser foot with the needle still in the fabric so I can pivot the fabric to sew the bottom of the zipper.
Now it's back up the other side.
Turn the garment right side out and use your best friend, the seam ripper, to pick out the basting and watch your zipper emerge.
I used a hook and eye to close the very top since the zipper didn't go all the way to the top.
Give it a good pressing and you're all done!