Using your zipper foot, slowly sew along the zipper.

If you don't have a zipper foot, you can use your regular foot, as shown below.  After you pin the fabric to the zipper, open the zipper halfway.  Sew about 1/8" away from the zipper.

When you reach the zipper pull, put the needle in the "down" position and lift up the foot.  Move the zipper pull to the top of the zipper.  Continue sewing to the end of the zipper.

Repeat for the other side of the zipper. 

When you are done, open out the pouch and cut out 1/2" squares from each corner of the pouch.  This will reduce bulk in the corners when the pouch is complete.