4. Now you're going to top stitch the zipper down. When I do this I like to top stitch only the outer piece down onto the zipper, keeping the lining out of the way. I also like to double my thread when I top stitch in a contrasting colour; it makes the stitching pop a little more and look deliberate. Just thread your machine like you normally would, but use two pieces of thread for your needle.
Leave the zipper foot on and stitch between the metal ends of the zipper. Do this on both pieces.