I guess I'll get off my soapbox now. The point of this post is to show you how to install a zipper using the lapped method. Although invisible zippers are the best ever, lapped zippers are far superior to center zippers. They may seem a bit more tricky, but practice a few and you'll get the hang of it.
Stitch seam leaving top open for zipper. Press left side seam allowance (when wrong side is facing up) back to 5/8" wide. Press right side seam allowance back to 1/2" wide. Make sure the 1/2" pressing goes all the way down past the point where the seam ends. This step is key to making this look right!
Turn piece so the right side of the fabric is facing up. Pin zipper right along the edge of opening that has been folded back 1/2". Match the pinked top of the zipper to the top of the fabric.
Info piece: All zippers are made to have about 3/4" extra tape at the top of the zipper. This makes it perfectly easy to install as most seam allowances are 5/8". It allows 1/8" give or take near the seam when the waistband is sewn in.
Pin all the way down past the point where the seam ends. Again-- this part is key.
Using a zipper foot, stitch very close to the edge of the zipper. Stitch past the point where the seam ends.
Note: This fabric is a knit, so that is why the stitching looks/is a not quite perfect. This part will end up being covered, so it doesn't exactly need to be perfect... unless you're doing it for a grade. :)
Fold the other side of the seam over the zipper. Cover the stitching.
Pin in place. Be sure to keep the pins on one side of the zipper as you may want to open the zipper while stitching.
Beginning at the place where the seam ends, stitch across the bottom of the zipper.
At about 3/8" from the folded edge, pivot and stitch along the zipper at 3/8". After stitching a couple inches, you may want to open the zipper so you can use the edge of the fabric as your guide in making a straight line.
Note: Now you only have to worry about one side being parallel instead of trying match everything perfectly!
Now you're ready for a waistband!