|To keep your centered zipper from slipping while inserting, use 1/8 inch wide basting tape to hold in place.
Baste the garment seam shut as per usual instructions. Put a strip of 1/8" wide basting tape down each side of the zipper tape on the right side. The tape needs to be parallel to the zipper teeth and should sit right on the stitching line. Remove the backing from the tape. Now, with the zipper closed, begin placing the zipper on the basted garment seam (wrong side of fabric). Starting from the bottom, roll the zipper up the seam, finger pressing both sides of the zipper tape as you roll and being careful to align the zipper teeth straight up the seam. You can now stitch your zipper in place from the right or wrong side (your preference). The zipper does not shift or slide - it will stay centered.