Open the zipper. With the garment wrong-side up, place the upside-down zipper (head facing down) over the seam allowance, aligning the teeth perfectly with the seam line.
If needed, create secure bottom stops by stitching across the zipper teeth multiple times to prevent the pull from coming off.
For visual learners, this video from Lauren's Top Tops shows the standard centered zip method, while this video from Professor Pincushion covers the process of installing a zipper in a seam. To make sure this fits your project, are you: (clothing) or a bag ? lb.zip
Pin the fabric pieces right-sides together and sew from the bottom up to the marked point where the zipper opening begins using a regular stitch.
Use a top-stitch for a clean, secure, and professional look. Open the zipper
Use Wonder Tape or pins to secure the zipper tape to the seam allowance.
Press the edges of the fabric where the zipper will be installed to create sharp, clean edges. For visual learners, this video from Lauren's Top
If assembling a zipper from a continuous chain, insert the slider head by cutting a small V into the zipper teeth, feeding both sides in, and pulling the slider up.